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Full text of "soil analysis"

Diagnosis and 
I m provem en t of 







United States Salinity Laboratory Staff 



Contri buti ng Authors: 



L. E. Allison 



J . W. Brown 
H. E. Hayward 
L. A. Richards 



L. Bernstein 
M. Fireman 
G. A. Pearson 
L. v. Wilcox 



C. A. Bower 
J . T. Hatcher 
R. C. Reeve 



L. A. Richards, Editor 

Soil and Water Conservation Research Branch 
Agricultural Research Service 

Agriculture Handbook No. 60 Issued February 1954 

UNITED STATES DEPARTMENT OF AGRICULTURE 



For sale by the Superintendent of Documents, U. S. Government Printing Office 

Washington 25, D. C. - Price $2.00 



Contents 



Page 

Chapter 1. Origin and nature of saline and alkali soils. 1 

S o u r c eSs of so uble salts. 3 

Salinization of soils. 3 

Alkali cation or accumulation of exchangeable sodium 

in soils . . 4 

Characteristics of saline and alkali soils, 4 

Saline soils 4 

Saline-alkali soils 5 

Nonsaline-alkali soils 5 

Chapter 2. Determination of the properties of saline 

and alkali soils 7 

Soil sampling. 7 

Estimation of soluble salts from electrical conduc- 
tivity 7 

Conductivity of the saturation extract and the 

saturation percentage 8 

Relation of conductivity to salt content and 

osmotic pressure 9 

Conductivity of 1:1 and 1:5 extracts. 13 

Salinity appraisal from the electrical resistance of 

soil paste 13 

Conversion of conductivity data to a standard ref- 
erence temperature 16 

Comparison of percent salt in soil and extract 

measurements 16 

Chemical determinations 17 

Soil reaction — pH 17 

Soluble cations and anions 18 

Solubleboron 19 

Exchangeable cations 19 

Gypsum 20 

Alkaline-earth carbonates (lime) 21 

Physical determinations 21 

Infiltration rate 21 

Permeability and hydraulic conductivity. 22 

Moisture retention by soil 23 

Density and porosity 23 

Aggregation and stability of structure 23 

Crust formation 25 

C hoi ce of deter mi nati ons and i nter pretati on of data. 25 
Equilibrium relations between soluble and ex- 
changeable cations. 25 

Chemical analyses of representative soil samples. 26 

Nonsaline-nonalkali soils 26 

Saline soils 26 

Nonsaline-alkali soils. 26 

Saline-alkali soils 30 

Cross-checking chemical analyses for consistency 

and reliability 30 

Factors that modify the effect of exchangeable 

sodium on sods 30 

Texture 30 

Surface area and type of clay mineral. 31 

Potassium status and soluble silicate 31 

Organic matter 31 

Sequence of determinations for soil diagnosis 33 

Chapter 3. Improvement and management of soils in 
arid and semiarid regions in relation to salinity 

and alkali 34 

Basic principles 34 

Irrigation and leaching in relation io salinity control. 34 

I rrigation 35 

Leaching 36 

Leaching requirement 37 

Leachingmethods 38 

Field leaching trials 39 

Special practices for salinity control 40 



Chapter 3-Continued 

Drainage of irrigated lands in relation to salinity 

control 

Drainage requirements. 

Water-transmission properties of soils. 

Boundary conditions 

Layout and placement of drains 

Techniques for drainage investigations, 

Measurements of hydraulic head 

Determination of subsoil stratigraphy 

Determination of water-transmitting properties 

of soils 

Chemical amendments for replacement of exchange- 
able sodium 

Suitability of various amendments under different 

soil conditions 

Chemical reactions of various amendments in 

alkali soils 

Class 1. Soils containing alkaline-earth car- 
bonates 

Class 2. Soils containing no alkaline-earth car- 
bonates; pH 7.5 or higher 

Class 3. Soils containing no alkaline-earth car- 
bonates; pH less than 7.5 

Estimation of amounts of various amendments 

needed for exchangeable-sodium replacement. 

Speed of reaction of amendments and economic 

considerations 

Application of amendments 

Laboratory and greenhouse tests as aids to diagnosis. 

Reclamation tests in the field 

Reclamation of saline and alkali soilsin humid regions. 

Chapter 4. Plant response and crop selection for saline 

and alkali soils 

Significance of indicator plants for saline soils 

Indicator plants, 

Crop response on saline soils, 

Salinity and water availability 

Specific ion effects 

SOdhim 

Calcium 

Magnesium 

Potassium 

Chloride 

Sulfate 

Bicarbonate 

Boron 

Plant analysis 

Crop selection for saline soils 

Germination 

Relative salt tolerance of crop plants 

Relative boron tolerance of crop plants 

Chapter 5. Quality of irrigation water 

Methods of analysis 

Characteristics that determine quality 

Electrical conductivity 

Sodium-adsorption-ratio 

Boron 

Bicarbonate 

Typical waters 

Classification of Irrigation waters, 

Salinity hazard 

Sodiumhazard 

Diagram for classifying irrigation waters 

Conductivity 

Sodium 

Effect of boron concentration on quality 

Effect of bicarbonate ion concentration on quality. 



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v 



VI 



CONTENTS 



Page 

Chapter 6. Methods for soil characterization 83 

SamiSing, soil extracts, and salinity appraisal 83 

(1) Soil sample collecting, handling, and sub- 

sampling. 83 

(2) Saturated soil paste 84 

(3) Soil-water extracts 84 

(3a) Saturation extract 84 

(3b) Twice-saturation extract for coarse-tex- 
tured soils (tentative). 88 

(3c) Soil-water extracts at 1:1 and 1:5 88 

(3d) Soil extract in the field-moisture range. . . 88 

(4) Electrical conductivity of solutions 89 

(4a) Standard Wheatstone bridge 89 

(4b) Direct indicating bridge 89 

(5) Resistance of soil paste and percent salt in 

soil. . . . 91 

(6) Freezing-point depression 91 

(6a) Freezing-point depression of solutions. ... 91 
(6h) Freezing-point depression of water in soil 

cores 93 

Soluble cations and anions 94 

(7) Calcium and magnesium by titration with 

ethyl enedi am inetetraacetate (Versenate). .. 94 

(8) Calcium by precipitation as calcium oxalate. 95 

(9) Magnesium by precipitation as magnesium 

ammonium phosphate 95 

(10) Sodium 96 

(10a) Sodium hy flame photometer 96 

(10b) Sodium by precipitation as sodium ttranyl 

zinc acetate 97 

(11) Potassium 97 

(Ma) Potassium by flame photometer 97 

(Mb) Potassium by precipitation as potassium 

dipicrylaminate 98 

(12) Carbonate and bicarbonate by titration with 

acid 98 

(13) Chloride by titration with silver nitrate. ... 98 

(14) Sulfate 99 

(14a) Sulfate by precipitation as barium sul- 
fate 99 

(14b) Sulfate by precipitation as calcium sul- 
fate 99 

(15) Nitrate by phenoldi sulfonic acid 100 

(16) Silicate as silicomolybdate 100 

(17) Boron 100 

Exchangeable cations 100 

(18) Exchangeable cations 100 

(19) Cation-exchange-capacity 101 

(20) Exchangeable-cation percentages-. 101 

(20a) Exchangeable-cation percentages by dr 

rect determination 101 

(20b) Estimation of exchangeable-sodium-per- 
centage and exchangeable-potassium - 

percentage from soluble cations 102 

Supplementary measurements 102 

(21) pH determinations 102 

(21a) pH reading of saturated soil paste 102 

(21b) pH reading of soil suspension 102 

(21c) pH reading of waters, solutions, and soil 

extracts 102 

(22) Gypsum 102 

(22a) Gypsum by precipitation with acetone 

(qualitative) 102 

(22b) Gypsum by precipitation with acetone 

(quantitative) 104 

(22c) Gypsum by increase in soluble calcium 

plus magnesium content upon dilution. 104 

(22d) Gypsum requirement 104 

(23) Alkaline-earth carbonates (lime) 105 

(23a) Alkaline-earth carbonates by effervescence 

with acid 105 

(23b) Alkaline-earth carbonates by gravimetric 

loss of carbon dioxide 105 

(23c) Alkaline-earth carbonates from acid neu- 
tralization 105 

(24) Organic matter 105 

(25) Total and external ethylene glycol retention. 106 



Paffe 

Chapter 6-Continued 

Soil water 107 

(26) Soil-moisture content 107 

(27) Saturation percentage 107 

(27a) Saturation percentage from oven-drying. 107 
(27b) Saturation percentage from volume of 

water added 107 

(27c) Saturation percentage from the weight 

of a known volume of paste 107 

(28) Infiltration rate 108 

(28a) Basin 108 

(28b) Cylinder 108 

(29) l/10-atmoss|lnei2 percentage 109 

(30) 1/3 -atmosphere percentage 109 

(31) 15-atmospflfiiBB percentage 109 

(32) Moisture-retention curve 110 

(33) Field-moisture range Ill 

(34) Hydraulic conductivity Ill 

(34a) Hydraulic conductivity of soil cores- .... Ill 

(34b) Hydraulic conductivity of disturbed soil. 112 
(34c) Hydraulic conductivity from piezometer 

measurements 113 

(34d) Hydraulic conductivity from auger-hole 

measurements 114 

(35) Hydraulic-head measurements in saturated 

soil 116 

(35a) Piesometers installed by driving 116 

(35b) Piezometers installed by jetting 117 

(35c) Observation wells uncased or with per- 
forated casing 117 

(36) Ground-water graphical methods 118 

(36a) Water-table contour maps 118 

(36b) Water-table isobath maps 118 

(36c) Profile flow patterns for ground water. . . 118 
(36d) Water-table isopleths for showing time 

variations in the elevation of the water 

table 119 

Physical measurements. . 120 

(37) Intrinsic permeability 120 

(37a) Permeability of soil to air 120 

(37b) Permeability of soil to water 121 

(38) Bulk density 121 

(39) Particle density 122 

(40) Porosity 122 

(41) Particle-size distribution 122 

(42) Aggregate-size distribution 124 

(42a) Wet sieving 124 

(42b) Aggregation of particles less than SO 

microns 125 

(43) M QJulus of rupture 126 

Chapter 7. Methods of plant culture and plant 

analysis 127 

Plant-culture techniques adapted to salt-tolerance 

investigations. 127 

(50) Artificially salinized field plots 127 

(51) Drum cultures 128 

(52) Sand and water cultures, 128 

Methods of plant analysis 128 

(53) Sampling and preparation of plant samples. - 128 

(54) Ashing 129 

(54a) Wet digestion 129 

(54b) Magnesium nitrate ignition 129 

(55) Calcium 129 

(55a) Calcium by flame photometer 129 

(55b) Calcium by oxalate method 130 

(56) Magnesium 130 

\ij I / i^vlUftU-H.l ■••*-•#*•*■**■»■-■■■»■ «■■■■■■■■■■■■■■■■■■■■ ■»■ 

(57a) Sodium by flame photometer 131 

(57b) Sodium by uranyl zinc acetate 131 

(58) Potassium 132 

(58a) Potassium by flame photometer 132 

(58b) Potassium by cobalti nitrite 132 

(59) Chloride 133 

(60) Sulfur 134 

(61) Phosphorus 134 

(62) Boron 134 



CONTENTS 



VII 



Chapter 8. Methods of analysis of irrigation waters. 

(70) Collection of irrigation water samples.. 

(71) Records, reports, and expression of results. 

(72) Electrical conductivity. 

(73) Boron 

(73a) Boron, electrometric titration. . 
(73b) Boron, colorimetric, using carmine. . 



(74) Dissolved 

(75) P H 
( 7 6 

(76a) 

(76b) 
(77) 
(78) 



of 



solids. 

waters. 

■ ■ ■ 

i I i c 
gravimetric, 
colorimetric 



) S 

Silica, 
Silica, 

Calcium. . . . 
Magnesium. . 

(79) Calcium and magnesium by the Versenate 

method 

(80) Sodium. 

(80a) Sodium by uranyl zinc acetate, gravi- 
metric. * 
(80b) Sodium by flame photometer. 



Page 

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143 
144 

144 
144 

144 
144 



Page 
Chapter 8-Continued 

(81) Potassium 144 

(81 a) Potassium by cohalti nitrite, gravimetric. 145 

(81b) Potassium by cobalti nitrite, volumetric. 145 

(81c) Potassium by flame photometer 145 

(82) Carbonate and bicarbonate., 145 

(83) Sulfate 1% 

(84) Chloride 146 

(8.5) Fluoride 147 

(86) Nitrate 147 

(86a) Nitrate, phenoldisulfonic acid 147 

(86b) Nitrate, Devarda 147 

Literature cited 148 

Glossary 154 

Appendix 157 

Symbols and abbreviations 157 

Conversion formulas and factors 157 

Chemical symbols, equivalent weights, and com- 
mon names 158 

Soil sampler and core retainer, 1.59 

Modulus of rupture apparatus. . 160 



Preface 

The Bankhead-Jones Act adopted by Congress in 1935 made funds available for agricultural research 
on a regional basis. At a meeting of representatives of the United States Department of Agriculture and the 
directors of the Agricultural Experiment Stations of 11 Western States, the decision was made to establish a 
salinity laboratory to conduct research on problems connected with the success and permanence of agriculture 
on saline and alkali soils. In 1937 the United States Regional Salinity Laboratory was established by the 
then Bureau of Plant Industry on grounds adjacent to its Rubidoux Laboratory in Riverside, Calif. A memo- 
randum of understanding, providing for official collaborators, was entered into with these 11 Western States and 
Hawaii. 

The Rubidoux Laboratory had been established by the Bureau's Division of Western Irrigation Agriculture 
in 1928 primarily to conduct research relating to the quality of water, with special emphasis on the toxicity 
of boron to plants. It was combined with the United States Regional Salinity Laboratory in 1948. 

In 1951 official cooperation and collaborator representation was extended to include the 17 Western States, 
and the name of the Laboratory modified to United States Salinity Laboratory. 

Close cooperative relations are maintained with the State Agricultural Experiment Stations and Hawaii 
through the official collaborators who meet annually to review the Laboratory's research program. 

The United States Salinity Laboratory is administered in the Agricultural Research Service. 

m 



Introduction 

Saline and alkali soil conditions reduce the value and productivity of considerable areas of land in the United 
States. The problem is an old one, and there is much information on this subject in the technical literature. 
It is the purpose of this handbook to bring together and summarize information that will be useful, particularly 
to professional agricultural workers, for the diagnosis and improvement of saline and alkali soils. 

The nomenclature for these problem soils is still in a formative stage. This is illustrated by the diversity 
of usage of such prominent investigators as Gedroiz (1917), Hilgard ( 1906 ),Hissink( 1933), Kelley (1948, 
1951), and De Sigmond (1938). Ultimate agreement on nomenclature will depend on the role of exchangeable 
potassium. The facts now available on this subject are meager, but they suggest that the undesirable physical 
properties that are characteristic of alkali soils are caused by excessive exchangeable sodium. Other elements 
of the alkali metal group either do not occur in significant quantities or do not appear to have similar action in 
soils. 

It is not the purpose of the writers to emphasize the definition of terms or to influence the usage of others; 
but, for clarity in the presentation of the subjects treated in this handbook, it was necessary to consider 
terminology, and a glossary of special terms has been included. In deference to past usage, the term "alkali 
soil" is employed to refer to soils that have a high exchangeable-sodium-percentage; and "saline soil" is used 
in connection with soils having a high value for the electrical conductivity of the saturation extract. 

This handbook was first issued in multilithed form in 1947, and it has been widely distributed in this 
country and abroad. 

No attempt is made to present a comprehensive review of the literature, because the handbook is intended 
primarily as a practical guide for those who are confronted with soil, plant, and water problems involving 
salinity and alkali. The first five chapters provide a basis for the evaluation and interpretation of measure- 
ments. The procedures and measuring methods given in chapters 6, 7, and 8 are those with which the Laboratory 
has had experience, and they are believed to have general applicability in the diagnosis and improvement of 
saline and alkali soils. 

There are other measuring methods in current use in various localities that have not been included, but no 
particular significance should be attached to this omission. It is wo* possible to cover all special methods, and 
it is always advisable to consult with the State agricultural experiment stations for detailed information on 
local problems. 

There is need for continued research on problems of saline and alkali soils and the many complicated inter- 
relations to crop production on these soils. The close cooperative relations of the Salinity Laboratory and the 
agricultural experiment stations of the 17 Western States and Hawaii have provided an efficient arrangement 
for conducting investigational work with a minimum of duplication of effort and for exchanging and 
disseminating research information. 

This handbook is the result of the combined efforts of the entire staff of the Salinity Laboratory. Those 
listed as authors have carried responsibility for writing various sections. Former staff members C. H. Wad- 
leigh and A. D. Ayers were among the authors of the earlier draft and assisted in reviewing the present one. 
The illustrations were prepared by Miles S. Mayhugh and R. H. Brooks. 

The writers are indebted to many reviewers, not all of whom are mentioned, who have offered helpful 
criticisms and suggestions. The sections relating to leaching and drainage in chapter 3 were reviewed by 
F. M. Eaton, Vaughn E. Hansen, 0. W. Israelsen, and Dean F. Peterson, Jr. W. C. Cooper, W. P. Cottam, 
F. M. Eaton, W. G. Harper, and W. J. Leighty reviewed chapter 4 and contributed suggestions relating to salt 
tolerance and indicator plants. Chapter 5 on quality of irrigation water was given special consideration by the 
collaborators, and this chapter was also reviewed by C. S. Scofield. Chapters 6, 7, and 8, dealing with methods, 
were reviewed by L. T. Alexander, B. J. Cooil, E. E. Frahm, J. C. Hide, A. J. MacKenzie, C. D. Moodie, 
A. H . Post, R. F. Reitemeier, and others. 

Special acknowledgment is made to the official collaborators of the Salinity Laboratory for their many helpful 
suggestions and for their cooperation and encouragement. The preliminary drafts of all sections of the handbook 
were made available to all collaborators, and the great majority of them responded with constructive criticisms 
and comments. 

H. E. Hay ward 

Director 

United States Salinity Laboratory 
Riverside, Calif. 
May 1953. 



Chapter 1 



Origin and Nature of Saline 
and Alkali Soils 



The soils under consideration in this handbook owe 
their distinctive character to the fact that they contain 
excessive concentrations of either soluble salts or ex- 
changeable sodium, or both. For agricultural pur- 
poses, such soils are regarded as a class of problem 
soils that requires special remedial measures and man- 
agement practices. Soluble salts produce harmful 
effects to plants by increasing the salt content of the soil 
solution and by increasing the degree of saturation of 
the exchange materials in the soil with exchangeable 
sodium. The latter effect occurs when the soluble con- 
stituents consist largely of sodium salts and is of a more 
permanent nature than the salt content of the soil solu- 
tion, since exchangeable sodium usually persists after 
the soluble salts are removed. 

In discussing these problem soils it is convenient to 
use terms that refer specifically to the two principal 
causes of the problem. "Saline soil," as used in this 
handbook, refers to a soil that contains sufficient soluble 
salts to impair its productivity. Similarly, alkali soils 
can be defined in terms of productivity as influenced by 
exchangeable sodium. In accordance with this usage, 
alkali soils may or may not contain excess soluble salts. 
Probably the most common problem involves soils that 
contain an excess of both soluble salts and exchange- 
able sodium, and, in agreement with the terminology of 
De Sigmond (1938) ,* these soils will be referred to as 
saline-alkali soils. 

The salt content of soils above which plant growth is 
affected depends upon several factors, among which are 
the texture of soil, the distribution of salt in the profile, 
the composition of the salt, and the species of plant. 
Several arbitrary limits for salinity have been suggested 
for distinguishing saline from nonsaline soils. Kear- 
ney and Scofield (1936), in discussing the choice of 
crops for saline lands, considered that plants begin to 
be adversely affected as the salt content of the soil ex- 
ceeds 0.1 percent. De Sigmond (1938) was in agree- 
ment with this limit. In the report of the United States 
National Resources Planning Board (1942, pp. 263- 
334) relative to the Pecos River investigation, Scofield 
considered a soil to be saline if the solution extracted 



from a saturated soil paste had an electrical conductiv- 
ity value of 4 mmhos/cm. or more. The electrical con- 
ductivity of the saturation extract was adopted by the 
Salinity Laboratory as the preferred scale for general 
use in estimating soil salinity. The Soil Survey Staff 
(1951) of the United States Department of Agriculture 
now uses either this method or the earlier method based 
on the electrical resistance of a sample of soil paste, 
the latter reading being converted to the dry-weight 
percentage of soluble salt in the soil. 

The decision regarding what level of exchangeable 
sodium in the soil constitutes an excessive degree of 
saturation is complicated by the fact that there is no 
sharp change in the properties of the soil as the degree 
of saturation with exchangeable sodium is increased. 
In the past an exchangeable-sodium-percentage of 15 
has been used at the Laboratory as a boundary limit 
between nonalkali and alkali soils. Insufficient data 
and experience are available to justify a change, but this 
limit must be regarded as somewhat arbitrary and ten- 
tative. In some cases, for example, 2 or 3 milliequiv- 
alents of exchangeable sodium per 100 gm. of soil has 
equal or even greater usefulness as a critical limit. 

There has been uncertainty in the past regarding the 
effect of exchangeable potassium on the physical prop- 
erties of soils and if, as De Sigmond (1928) and Magi- 
stad (1945) have proposed, exchangeable sodium and 
potassium should be considered as additive in defining 
alkali soils. It has been observed in several instances 
that alkali soils high in exchangeable potassium have 
better physical properties and are more readily reclaim- 
able than other alkali soils containing similar amounts 
of exchangeable sodium but low amounts of exchange- 
able potassium. The view that exchangeable potassium 
has only a slight or no adverse effect upon the physical 
properties of soils is supported by the results of meas- 
urements made recently at the Laboratory 2 on samples 
of seven soils adjusted to various levels of exchangeable 
sodium and exchangeable potassium (fig. 1). 

The magnitude of the air: water permeability ratio 
is a measure of the extent to which soil structure 
deteriorates when water is applied, a high ratio indi- 
cating a high degree of deterioration. The data for 



1 References to Literature Cited (p. 148) are herein indicated 
by the name of the author (or authors) followed by the year of 
publication. 



2 Unpublished data by R. C. Reeve, C. A. Bower, R. H. Brooks, 
and F. B. Gschwend. 

1 



AGRICULTURE HANDBOOK 60, U. S. DEPT. OF AGRICULTURE 



1000 



<t 800 



oc 6oO 



400 



200 



1 — 


CHINO 




2- 


HUNTLEY (EXPT. 


STA.) 


3 — 


SEBREE 




4- 


-AIKEN 




5 — 


CHILCOTT 




6 — 


■ESQUATZEL 




7 — 


-TRAVER 






1 



I 



o 
o 



20 40 60 80 

EXCHANGEABLE— SODIUM— PERCENTAGE 



100 



200 




20 40 60 

EXCHANGEABLE -POTASSIUM 



80 
PERCENTAGE 



100 



Figure 1.— Relative effect of exchangeable sodium and exchangeable potassium on the ratio of the air permeability to the water 

permeability of soils. 



SALINE AND ALKALI SOILS 



two soils are not plotted in the graph showing the 
effect of the exchangeable-potassium-percentage, be- 
cause they nearly coincide with the lower curve. In 
general, the increase in ratio with increase in exchange- 
able sodium is directly related to the total specific 
surface of the soils. 

Improvements are being made in methods of apprais- 
ing both the susceptibility and the status of soils with 
respect to the injurious effects of exchangeable sodium. 
For these reasons, both the terminology and the classi- 
fication limits for alkali soils must be regarded as being 
in a transitional stage. 

Sources of Soluble Salts 

The soluble salts that occur in soils consist mostly of 
various proportions of the cations sodium, calcium, and 
magnesium, and the anions chloride and sulfate. Con- 
stituents that ordinarily occur only in minor amounts 
are the cation potassium and the anions bicarbonate, 
carbonate, and nitrate. The original and, to some ex- 
tent, the direct source of all the salt constituents are the 
primary minerals found in soils and in the exposed 
rocks of the earth's crust. Clarke (1924) has estimated 
that the average chlorine and sulfur content of the 
earth's crust is 0.05 and 0.06 percent, respectively, while 
sodium, calcium, and magnesium each occur to the ex- 
tent of 2 or 3 percent. During the process of chemical 
weathering, which involves hydrolysis, hydration, solu- 
tion, oxidation, and carbonation, these constituents are 
gradually released and made soluble. 

Bicarbonate ions form as a result of the solution of 
carbon dioxide in water. The carbon dioxide may be 
of atmospheric or biological origin. Water contain- 
ing carbon dioxide is a particularly active chemical 
weathering agent that releases appreciable quantities 
of the cation constituents as the bicarbonates. Carbon- 
ate and bicarbonate ions are interrelated, the relative 
amounts of each present being a function of the pH 
value of the solution. Appreciable amounts of carbon- 
ate ions can be present only at pH values of 9.5 or 
higher. 

While the above-mentioned salt constituents are of 
most importance in saline soils, there are places, as in 
parts of Colorado, Utah, and Washington, where high 
concentrations of nitrate are found. Various theories 
(Kelley, 1951) have been proposed to explain the origin 
of excessive nitrate salts in soils. Boron, owing to its 
marked toxicity to plants when present even in low con- 
centrations, also deserves mention (Eaton and Wilcox, 
1939). The principal source of this element is the 
mineral tourmaline, which is a rather widespread but 
minor constituent of primary rocks. 

Although weathering of primary minerals is the indi- 
rect source of nearly all soluble salts, there are probably 
few instances where sufficient salts have accumulated in 
place from this source alone to form a saline soil. 
Saline soils usually occur in areas that receive salts 
from other locations, and water is the primary carrier. 
The ocean may be the source of salts as in soils where 
the parent material consists of marine deposits that were 



laid down during earlier geologic periods and have 
since been uplifted. The Mancos shales occurring in 
Colorado, Wyoming, and Utah are typical examples of 
saline marine deposits. The ocean is also the source 
of the salts in low-lying soils along the margin of sea- 
coasts. Sometimes salt is moved inland through the 
transportation of spray by winds and is called cyclic 
salt (Teakle, 1937) . More commonly, however, the 
direct source of salts is surface and ground waters. All 
of these waters contain dissolved salts, the concentration 
depending upon the salt content of the soil and geologic 
materials with which the water has been in contact. 
Waters act as sources of salts when used for irrigation. 
They may also add salts to soils under natural con- 
ditions, as when they flood low-lying land or when 
ground water rises close to the soil surface. 

Salinization of Soils 

Saline soils occur for the most part in regions of arid 
or semiarid climate. Under humid conditions the solu- 
ble salts originally present in soil materials and those 
formed by the weathering of minerals generally are car- 
ried downward into the ground water and are' trans- 
ported ultimately by streams to the oceans. Saline soils 
are, therefore, practically nonexistent in humid regions, 
except when the soil has been subjected to sea water in 
river deltas and other low-lying lands near the sea. In 
arid regions leaching and transportation of soluble salts 
to the ocean is not so complete as in humid regions. 
Leaching is usually local in nature, and soluble salts 
may not be transported far. This occurs not only be- 
cause there is less rainfall available to leach and trans- 
port the salts but also because of the high evaporation 
rates characteristic of arid climates, which tend further 
to concentrate the salts in soils and in surface waters. 

Restricted drainage is a factor that usually contrib- 
utes to the salinization of soils and may involve the pres- 
ence of a high ground-water table or low permeability 
of the soil. The high ground-water table is often re- 
lated to topography. Owing to the low rainfall in 
arid regions, surface drainageways may be poorly de- 
veloped. As a consequence, there are drainage basins 
that have no outlet to permanent streams. The drain- 
age of salt-bearing waters away from the higher lands 
of the basin may raise the ground-water level to the soil 
surface on the lower lands, may cause temporary flood- 
ing, or may form permanent salty lakes. Under such 
conditions upward movement of saline ground water or 
evaporation of surface water results in the formation 
of saline soil. The extent of saline areas thus formed 
may vary from a few acres to hundreds of square miles. 
M any of the saline soils in the G reat Basin were formed 
in this manner. Similar areas occur throughout the 
Western States. They are often referred to as play as 
or dry lakes. 

Low permeability of the soil causes poor drainage 
by impeding the downward movement of water. 
Low permeability may be the result of an unfavorable 
soil texture or structure or the presence of indurated 
layers. The latter may consist of a claypan, a caliche 



AGRICULTURE HANDBOOK 6 0, U. S. DEPT. OF AGRICULTURE 



layer, or a silica hardpan. De Sigmond (1924) con- 
sidered the presence of an impermeable soil layer essen- 
tial for the formation of the saline soils found in 
Hungary. 

The salinity problem of principal economic impor- 
tance arises when previously nonsaline soil becomes 
saline as the result of irrigation. Such soils are often 
located in valleys adjacent to streams, and, because of 
the ease with which they can be irrigated, the more 
level areas are usually selected for cultivation. While 
such soils may be well drained and nonsaline under 
natural conditions, the drainage may not be adequate 
for irrigation. When bringing new lands under irri- 
gation, farmers have frequently failed to recognize the 
need for establishing artificial drains to care for the 
additional water and soluble salts. As a result, the 
ground-water table may rise from a considerable depth 
to within a few feet of the soil surface in a few years. 
During the early development of irrigation projects, 
water is frequently plentiful and there is a tendency to 
use it in excess. This hastens the rise of the water table. 
Waters used for irrigation may contain from 0.1 to as 
much as 5 tons of salt per acre-foot of water, and the 
annual application of water may amount to 5 feet or 
more. Thus, considerable quantities of soluble salts 
may be added to irrigated soils over relatively short 
periods of time. When the water table rises to within 
5 or 6 feet of the soil surface, ground water moves 
upward into the root zone and to the soil surface. 
Under such conditions, ground water, as well as irriga- 
tion water, contributes to the salinization of the soil. 

Alkalization or Accumulation of Exchange- 
able Sodium in Soils 

Soil particles adsorb and retain cations on their sur- 
faces. Cation adsorption occurs as a consequence of 
the electrical charges at the surface of the soil particles. 
While adsorbed cations are combined chemically with 
the soil particles, they may be replaced by other cations 
that occur in the soil solution. The reaction whereby a 
cation in solution replaces an adsorbed cation is called 
cation exchange. Sodium, calcium, and magnesium 
cations are always readily exchangeable. Other cat- 
ions, like potassium and ammonium, may be held at 
certain positions on the particles in some soils so that 
they are exchanged with great difficulty and, hence, 
are said to be fixed. 

Cation adsorption, being a surface phenomenon, is 
identified mainly with the fine silt, clay, and organic 
matter fractions of soils. Many different kinds of min- 
erals and organic materials occurring in soils have 
exchange properties and together are referred to as the 
exchange complex. The capacity of a soil to adsorb 
and exchange cations can be measured and expressed 
in chemical equivalents and is called the cation-ex- 
change-capacity. It is commonly expressed in milli- 
equivalents per 100 gm. of soil. Various chemical and 
physical factors interact to make the measured value 
depend somewhat on the method of determination, but, 
nevertheless, the cation-exchange-capacity is a reason- 



ably definite soil property that has considerable prac- 
tical significance. I n view of the fact that the adsorbed 
cations can interchange freely with adjacent cations 
in the soil solution, it is to be expected that the propor- 
tion of the various cations on the exchange complex 
will be related to their concentrations in the soil 
solution. 

Calcium and magnesium are the principal cations 
found in the soil solution and on the exchange complex 
of normal soils in arid regions. When excess soluble 
salts accumulate in these soils, sodium frequently be- 
comes the dominant cation in the soil solution. Thus, 
sodium may be the predominant cation to which the soil 
has been subjected, or it may become dominant in the 
soil solution, owing to the precipitation of calcium and 
magnesium compounds. As the soil solution becomes 
concentrated through evaporation or water absorption 
by plants, the solubility limits of calcium sulfate, cal- 
cium carbonate, and magnesium carbonate are often 
exceeded, in which case they are precipitated with a 
corresponding increase in the relative proportion of 
sodium. Under such conditions, a part of the original 
exchangeable calcium and magnesium is replaced by 
sodium. 

From a practical viewpoint, it is fortunate that the 
calcium and magnesium cations in the soil solution are 
more strongly adsorbed by the exchange complex than 
sodium. At equivalent solution concentrations, the 
amounts of calcium and magnesium adsorbed are sev- 
eral times that of sodium. In general, half or more of 
the soluble cations must be sodium before significant 
amounts are adsorbed by the exchange complex. In 
some saline soil solutions, however, practically all of 
the cations are sodium, and in these sodium is the pre- 
dominant adsorbed cation. 

Characteristics of Saline and Alkali Soils 

The term "soil" is used in several senses by agricul- 
turists. In one sense a soil is considered to be a three- 
dimensional piece of landscape having shape, area, and 
depth (Soil Survey, 1951). The concept of a soil as a 
profile having depth but not necessarily shape or area 
is also a common use of the term. In another sense, 
often used in this handbook, the term is applied to 
samples representing layers or points in the profile. 
Saline and alkali soils are defined and diagnosed on the 
basis of determinations made on soil samples, and the 
significance of information thus obtained contributes 
substantially to scientific agriculture. The extension 
and harmonization of these definitions to the problems 
and purposes of soil survey and soil classification have 
not been attempted, because it lies somewhat beyond 
the scope of the present work. 

To facilitate and clarify this discussion, the problem 
soils under consideration have been separated into three 
groups : Saline, saline-alkali, and nonsaline-alkali 
soils. 

Saline Soils 

Saline is used in connection with soils for which the 
conductivity of the saturation extract is more than 4 



SALINE AND ALKALI SOILS 



mmhos/cm. at 25" C. and the exchangeable-sodium- per- 
centage is less than 15. Ordinarily, the pH is less than 
8.5. These soils correspond to H ilgard's (1906) "white 
alkali" soils and to the "Solonchaks" of the Russian soil 
scientists. When adequate drainage is established, the 
excessive soluble salts may be removed by leaching and 
they again become normal soils. 

Saline soils are often recognized by the presence of 
white crusts of salts on the surface. Soil salinity may 
occur in soils having distinctly developed profile char- 
acteristics or in undifferentiated soil material such as 
alluvium. 

The chemical characteristics of soils classed as saline 
are mainly determined by the kinds and amounts of 
salts present. The amount of soluble salts present con- 
trols the osmotic pressure of the soil solution. Sodium 
seldom comprises more than half of the soluble cations 
and hence is not adsorbed to any significant extent. The 
relative amounts of calcium and magnesium present in 
the soil solution and on the exchange complex may 
vary considerably. Soluble and exchangeable potas- 
sium are ordinarily minor constituents, but occasionally 
they may he major constituents. The chief anions are 
chloride, sulfate, and sometimes nitrate. Small 
amounts of bicarbonate may occur, but soluble carbo- 
nates are almost invariably absent. In addition to the 
readily soluble salts, saline soils may contain salts of 
low solubility, such as calcium sulfate (gypsum) and 
calcium and magnesium carbonates (lime) . 

Owing to the presence of excess salts and the absence 
of significant amounts of exchangeable sodium, saline 
soils generally are flocculated; and, as a consequence, 
the permeability is equal to or higher than that of 
similar nonsaline soils. 

Saline-Alkali Soils 

Saline-alkali is applied to soils for which the con- 
ductivity of the saturation extract is greater than 4 
mmhos/cm. at 25" C. and the exchangeable-sodium- 
percentage is greater than 15. These soils form as a 
result of the combined processes of salinization and 
alkalization. As long as excess salts are present, the 
appearance and properties of these soils are generally 
similar to those of saline soils. Under conditions of 
excess salts, thepH readings are seldom higher than 8.5 
and the particles remain flocculated. If the excess solu- 
ble salts are leached downward, the properties of these 
soils may change markedly and become similar to those 
of nonsaline-alkali soils. As the concentration of the 
salts in the soil solution is lowered, some of the ex- 
changeable sodium hydrolyzes and forms sodium hy- 
droxide. This may change to sodium carbonate upon 
reaction with carbon dioxide absorbed from the at- 
mosphere. In any event, upon leaching, the soil may 
become strongly alkaline (pH readings above 8.5) , the 
particles disperse, and the soil becomes unfavorable for 
the entry and movement of water and for tillage. Al- 
though the return of the soluble salts may lower the 
pH reading and restore the particles to a flocculated 
condition, the management of saline-alkali soils contin- 



ues to be a problem until the excess salts and exchange- 
able sodium are removed from the root zone and a 
favorable physical condition of the soil is reestablished. 
Saline-alkali soils sometimes contain gypsum. When 
such soils are leached, calcium dissolves and the re- 
placement of exchangeable sodium by calcium takes 
place concurrently with the removal of excess salts. 

Nonsaline-Alkali Soils 

Nonsaline-alkali is applied to soils for which the ex- 
changeable-sodium-percentage is greater than 15 and 
the conductivity of the saturation extract is less than 4 
mmhos/cm. at 25" C. ThepH readings usually range 
between 8.5 and 10. These soils correspond to Hil- 
gard's "black alkali" soils and in some cases to "Solo- 
netz," as the latter term is used by the Russians. They 
frequently occur in semiarid and arid regions in small 
irregular areas, which are often referred to as "slick 
spots." Except when gypsum is present in the soil or 
the irrigation water, the drainage and leaching of saline- 
alkali soils leads to the formation of nonsaline-alkali 
soils. As mentioned in the discussion of saline-alkali 
soils, the removal of excess salts in such soils tends to 
increase the rate of hydrolysis of the exchangeable 
sodium and often causes a rise of the pH reading of 
the soil. Dispersed and dissolved organic matter pres- 
ent in the soil solution of highly alkaline soils may be 
deposited on the soil surface by evaporation, thus caus- 
ing darkening and giving rise to the term "black alkali." 

If allowed sufficient time, nonsaline-alkali soils de- 
velop characteristic morphological features. Because 
partially sodium-saturated clay is highly dispersed, it 
may be transported downward through the soil and ac- 
cumulate at lower levels. As a result, a few inches of 
the surface soil may be relatively coarse in texture and 
friable; but below, where the clay accumulates, the soil 
may develop a dense layer of low permeability that 
may have a columnar or prismatic structure. Com- 
monly, however, alkali conditions develop in such soils 
as a result of irrigation. In such cases, sufficient time 
usually has not elapsed for the development of the 
typical columnar structure, but the soil has low per- 
meability and is difficult to till. 

The exchangeable sodium present in nonsaline-alkali 
soil may have a marked influence on the physical and 
chemical properties. As the proportion of exchange- 
able sodium increases, the soil tends to become more 
dispersed. The pH reading may increase, sometimes 
becoming as high as 10. The soil solution of non- 
saline-alkali soils, although relatively low in soluble 
salts, has a composition that differs considerably from 
that of normal and saline soils. While the anions 
present consist mostly of chloride, sulfate, and bicar- 
bonate, small amounts of carbonate often occur. At 
high pH readings and in the presence of carbonate ions, 
calcium and magnesium are precipitated; hence, the 
soil solutions of nonsaline-alkali soils usually contain 
only small amounts of these cations, sodium being the 
predominant one. Large quantities of exchangeable 
and soluble potassium may occur in some of these soils. 



6 



AGRICULTURE HANDBOOK 60, U. S. DEPT. OF AGRICULTURE 



The effect of excessive exchangeable potassium on soil 
properties has not been sufficiently studied. 

Nonsaline-alkali soils in some areas of western 
United States have exchangeable-sodium-percentages 
considerably above 15, and yet the pH reading, espe- 
cially in the surface soil, may be as low as 6. These soils 



have been referred to by De Sigmond (1938) as de- 
graded alkali soils. They occur only in the absence 
of lime, and the low pH reading is the result of ex- 
changeable hydrogen. The physical properties, how- 
ever, are dominated by the exchangeable sodium and 
are typically those of a nonsaline-alkali soil. 



Chapter 2 



Determination of the Properties 
of Saline and Alkali Soils 



This chapter discusses determinations that give in- 
formation on the chemical and physical properties of 
saline and alkali soils and thus serve as a basis for their 
diagnosis, treatment, and management. The status of 
knowledge on this subject is such that it is not yet pos- 
sible to prepare a brief handbook containing a few 
simple measurements that will give all the necessary in- 
formation. A number of different types of measure- 
ments are presented. Some of these must be regarded 
as tentative and subject to change and improvement. 
In some cases alternate procedures are proposed, and 
the individual worker will need to decide what kind 
and how many measurements will be required for the 
problem at hand. The purpose, application, and inter- 
pretation of the various determinations are discussed in 
this chapter. Detailed directions for making the 
measurements are given in chapter 6. 

Soil Sampling 

There is no standard procedure for obtaining soil 
samples for appraising salinity and alkali. Usually the 
details of procedure will depend upon the purpose for 
which the sample is taken. If the objective is to obtain 
a general evaluation of salinity in a given area, the 
average salt content of a number of samples provides 
an index for the over-all appraisal. The variation 
among samples gives an index of the variation in salt 
content that may be encountered in the field. The 
larger the number of samples, the more accurate the 
appraisal will be. Too few samples may give a com- 
pletely erroneous index of the salinity status. The 
deviation between the actual conditions existing in an 
area and the evaluation of the situation from the 
sampling procedure is designated as the "sampling 
error." It is evident that the larger the number of 
samples and the more carefully they are selected, the 
smaller the sampling error will be. 

Salt concentration in soils may vary greatly with 
horizontal or vertical distance and with time. The na- 
ture of the soil, microrelief, and the cause and source 
of salinity should be considered. Factors that cause 
migration of salt, such as seasonal precipitation, irriga- 
tion, and phase in the crop cycle, should be taken into 
account in relation to the time of sampling. In culti- 
vated areas, soil management history may be the most 



important single factor in determining salinity status, 
and field boundaries may enter the problem of where 
to sample and how to composite the samples. 

The interpretation and use of salinity and alkali 
measurements necessarily depend on the completeness 
and accuracy of observational data recorded at the time 
of sampling. A record of the species and condition of 
the plant cover is of particular importance. When at- 
tempting to correlate crop conditions in the field with 
soil -salinity measurements, it is necessary to take 
samples from the active root zone of the plants. 

The following suggestions are offered on where and 
how to sample: 

(a) Visible or suspected salt crusts on the soil 
surface should be sampled separately and the 
approximate depth of sample recorded. 

(b) If the soil shows evidence of profile develop- 
ment or distinct stratification, samples should 
betaken by horizons or layers. 

(c) In the absence of profile development or dis- 
tinct stratification, the surface samples (ex- 
cluding the surface crust) should be taken to 
the plow depth, usually to a depth of 6 or 7 
inches. 

(d) Succeeding samples may betaken at intervals 
of 6 to 18, 18 to 36, and 36 to 7.2 inches, or 
other convenient depths, depending on the 
depth of the root zone, the nature of the prob- 
lem, and the detail required. 

(e) Sometimes soil samples taken for salinity 
and alkali determinations may be composited 
to reduce analytical work. 

(/) The size of samples will depend on the meas- 
urements that are to be made. 

Detailed suggestions on taking and handling soil 
samples along with a sample of the field data sheet used 
at the Salinity Laboratory are given in Method 1. 

Estimation of Soluble Salts From Electrical 

Conductivity 

The choice of a method for measuring salinity de- 
pends on such things as the reason for making the meas- 
urements, the number of samples to be handled, and the 
time and effort available for doing the work. Accurate 

7 



8 



AGRICULTURE HANDBOOK 60, U. S. DEPT. OF AGRICULTURE 



methods usually require more time and, therefore, 
limit the number of determinations. 

Electrical-resistance measurements can be made 
quickly and accurately and have long been used for esti- 
mating soluble salts in soil (Whitney and Means, 1897) ; 
however, electrical conductance, which is the recipro- 
cal of resistance, is more suitable for salinity measure- 
ments, because it increases with salt content, thus 
simplifying the interpretation of readings. Moreover, 
expressing results in terms of specific conductance or 
conductivity makes the determination independent of 
the size and shape of the sample. 

Electrical conductance is expressed in mhos, i. e., 
reciprocal ohms, while electrical conductivity has the 
dimensions of mhos per centimeter. I n this handbook, 
the symbol "EC" is used to represent electrical conduc- 
tivity. 3 

The salt content of the soil can be estimated roughly 
from an electrical-conductivity measurement on a satu- 
rated soil paste or a more dilute suspension of soil in 
water. A better estimate of soluble salts can be ob- 
tained from the conductivity of a water extract of the 
soil. In general the higher the moisture content, the 
easier it will be to obtain the extract, but the less repre- 
sentative the extracted solution will be of the solution 
to which plant roots are exposed in the soil. 

Soil solutions in the field -moisture range can be ex- 
tracted for study and analysis by the displacement 
method (White and Ross, 1937) or with the pressure- 
membrane apparatus (Method 3d). These methods are 
used mainly for research and special chemical studies. 

Plants in saline soil are responsive to the concentra- 
tion of the soil solution, and the relation of concentra- 
tion to the normal field-moisture range is sometimes 
overlooked. There is more than a tenfold range in the 
wilting percentage of various soils. Consequently, the 
Geld-moisture range may vary greatly from one soil to 
another. For example, a sand and a clay could have 
the same soluble-salt content expressed as percent, dr> 
weight basis, but the soil -solution concentration when 
near the wilting percentage could be 10 times as high 
for the sand as for the clay. 



3 The standard unit for conductivity (mho /cm.) is a large unit, 
so that most solutions have a conductivity that is much less than 
one unit. For instance, a measurement on one sample of water 
from the Rio Grande at the Elephant Butte Dam gave EC= 
0.000694 mho/cm. For such cases, with physical and chemical 
measurements, it is customary to choose a small subunit that 
gives a more convenient location of the decimal point when 
recording or expressing data. For example, the unit ECxW 
is called the millimho per centimeter. This is a convenient, 
practical conductivity unit for most soil salinity work. Until 
recently ECXW (or £X10 S ) has been in common use. 
ECX 10" designates conductivity expressed in micromhos per 
centimeter. This is the unit most generally used for expressing 
the conductivity of waters. The conductivity of the Rio Grande 
sample mentioned above, when expressed in these various units, 
is: 

EC= 0.000694 mho /cm. 
ECX 10 :, =0.694millimho/cm. 
ECX 10 5 =69.4(=KX10 B ) 
EC X 10^694 micromhos/cm. 



Conductivity of the Saturation Extract and the 

Saturation Percentage 

The conductivity of the saturation extract is recom- 
mended as a general method for appraising soil salinity 
in relation to plant growth. The method is somewhat 
less rapid than a resistance measurement of the soil 
paste, but the result is easier to relate to plant response. 
The procedure involves preparing a saturated soil paste 
by stirring, during the addition of distilled water, until 
a characteristic endpoint is reached. A suction filter 
is then used to obtain a sufficient amount of the extract 
for making the conductivity measurement. 

The special advantage of the saturation-extract 
method of measuring salinity lies in the fact that the 
saturation percentage is directly related to the field- 
moisture range. In the field, the moisture content of 
the soil fluctuates between a lower limit represented 
by the permanent-wilting percentage and the upper, 
wet end of the available range, which is approxi- 
mately two times the wilting percentage. Measure- 
ments on soils indicate that over a considerable 
textural range the saturation percentage (SP) is ap- 
proximately equal to four times the 15-atmosphere 
percentage (FAP), which, in turn, closely approximates 
the wilting percentage. The soluble-salt concentration 
in the saturation extract, therefore, tends to be about 
one-half of the concentration of the soil solution at the 
upper end of the field-moisture range and about one- 
fourth the concentration that the soil solution would 
have at the lower, dry end of the field-moisture range. 
The salt-dilution effect that occurs in fine-textured soils, 
because of their higher moisture retention, is thus auto- 
matically taken into account. For this reason, the 
conductivity of the saturation extract (EC,) can be 
used directly for appraising the effect of soil salinity on 
plant growth. 

Table 1 gives some of the experimental data sup- 
porting the foregoing statements. Since the 15-atmos- 
phere percentage appears to be the most significant 
moisture property that can be readily measured, this 
retentivity value was used to separate soil samples into 
three textural groups: Coarse, medium, and fine (table 
1). The FAP ranges arbitrarily selected to designate 
these textural groups were: Coarse, 2.0-6.5; medium, 
6.6-15.0; and fine, greater than 15.1. The numbers in 
the FAP column of table 1 are the actual FAP values 
for the available samples in the various textural groups. 
The SP/FAP ratio of the medium-textured group, 
which is largest in number, is approximately 4 and the 
standard deviation is small; whereas the ratios for 
the fine-textured and high organic matter groups are 
somewhat lower (Campbell and Richards, 1950). 

The saturation percentage for sands, when determined 
by the standard procedure, gives values that, relative 
to the field-moisture range, are higher than for other 
soils. This occurs because in sands the large pores that 
are filled with water at the saturation-paste condition 
do not correspondingly retain water under field condi- 
tions. Consequently, EC e Xl0 3 for sands, when re- 
ferred to the regular saturation-extract scale, gives an 



SALINE AND ALKALI SOILS 



9 



Table I. -Relation of saturation percentage (SP) to IS -atmosphere percentage (FAP)as influenced by soil 

texture 



Soil group 



Coarse . . 
Medium 

Fine 

Organic . 



Soil 
samples 



Number 
10 
23 
11 
18 



FAP 



Mini- 
mum 




Maxi- 
mum 



6.5 
14.2 
21.0 
51.3 



Aver- 
age 



5.0 
10.8 
18.5 
37.9 



SP 



SP/FAP 



optimistic index of salinity, i. e., underrates the salinity 
condition. Method 3b gives a tentative procedure for 
estimating the upper limit of the field-moisture range. 
From this, a moisture content for extraction is deter- 
mined and a procedure for obtaining a conductivity 
value that can be used on the regular saturation -extract 
scale is suggested. This new procedure is tentative 
because it has not been subjected to extensive testing, 
but it has given good results for soils with SP values 
of approximately 25 or less. 

It would be more reliableto appraise salinity by using 
measurements of extracts of the soil solution in the 
field-moisture range. However, difficulty of obtaining 
such extracts would make them prohibit&efor routine 
use. The next higher feasible moisture content appears 
to be the saturation percentage. The following scale 
is recommended for general use in appraising the 
effect of soluble salts on crops. It shows the relation 
of crop response to soil salinity expressed in terms 
of the conductivity of the saturation extract. 

Use of the conductivity of the saturation extract as 
an index of soil salinity was introduced attheRubidoux 
Laboratory in 1939 for the Pecos River Joint Investi- 
gation. The salinity scale given in the earlier draft of 
this handbook was substantially the same as the scale 
originally proposed by Sconeld in his report on the 
Pecos River Joint Investigation (United States National 
Resources Planning Roard, 1942, pp. 263334). The 
scale given here has been modified somewhat from 
those previously used. 

It is often desirable, because of the extra informa- 
tion provided on soil texture and moisture retention, 
to determine the soil-moisture content at saturation, 
i. e., the saturation percentage (SP) when saturated 
soil paste is prepared for salinity measurements. A 
rapid procedure for SP determination based on the 



Mini- 
mum 



16.0 
26.4 
41.8 
81.0 



Maxi- 
mum 



43.1 
60.0 
78.5 
255 



Aver- 
age 



Mini- 
mum 



31.8 

42.5 
59.5 
142 



4.68 
3.15 
2.03 
2.53 



Maxi- 
mum 



8.45 
5.15 
4.26 
4.97 



Aver- 


Stand- 




ard de- 


age 


viation 


6.37 


1. 15 


3.95 


.48 


3.20 


.60 


3.66 


.75 



weight of a known volume of saturated paste has been 
described by Wilcox (1951) and is included as 
Method 27c. 

The end point for mixing a saturated soil paste is 
reasonably definite; and, with a little training, good 
agreement can be obtained among various operators. 
Slight variations in technique, such as adding prac- 
tically all the water to the soil sample before stirring 
or adding the air-dry soil to a known amount of water, 
do not appreciably affect the saturation percentage of 
most soils. Special precautions, however, must be 
taken with very fine and very coarse textured soils. 
For example, in some clay soils the amount of water 
that must be added to bring about saturation can be 
varied 10 percent or more, depending upon the rate of 
adding water and the amount of stirring. The more 
rapid the rate of water addition in relation to stirring, 
the lower the saturation percentage may be. The lower 
value is desirable to reduce the time and effort during 
mixing and also to minimize puddling of the soil. 
Campbell and Richards (1950) found that the con- 
ductivity of the saturation-extract method is applicable 
also for the measurement of salinity in peat soils. With 
air-dried peats, an overnight wetting period is necessary 
to obtain a definite endpoint for the saturated paste. 

Relation of Conductivity to Salt Content and 

Osmotic Pressure 

The relation between the electrical conductivity and 
the salt content of various solutions is shown graphically 
in several figures. The curves (fig. 2) for the chloride 
salts and Na 2 S0 4 almost coincide, but MgS0 4 ,CaS0 4 , 
and NaHC0 3 have lower conductivities than the other 
salts at equivalent concentrations. When the concen- 
tration is given in percent salt or parts per million, 
the curves (fig. 3) are more widely separated. 



Salinity effects mostly 
negligible 



Yields of very sensitive 
crops may be restricted 



Yields of many crops 
restricted 



Only tolerant crops 

yield satisfactorily 



Only a few very tolerant 

crops yield satisfactorily 



4 8 

Scale of conductivity (millimhos per centimeter at 25° C.) 



16 



259525 O - 54 - 2 



10 



AGRICULTURE HANDBOOK 60, U. S. DEPT. OF AGRICULTURE 



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40 



CONDUCTIVITY 



MILLIMHOS /CM. (ECxIO^) AT 25° C. 



Figure 2. -Concentration of single-salt solutions in milliequivalents per liter as related to electrical conductivity. 



With soils from widely separated areas in western 
United States, the concentration range was higher 
(fig. 4) than that shown in figures 2 and 3 ; conse- 
quently, the electrical conductivity is expressed in mil- 
limhos per centimeter. This is a convenient unit to use 
for extracts from saline soils. Soils represented by 
points that are considerably above the average line 
usually contain a relatively high amount of calcium or 
magnesium sulfate. Information on the salt content 
of irrigation water in relation to electrical conductivity 
is given in chapter 5. 



Experimental work conducted at the Salinity Labora- 
tory by Hayward and Spurr (1944),Wadleigh and 
Ayers ( 1945) , and workers elsewhere indicates that the 
osmotic pressure of the soil solution is closely related 
to the rate of water uptake and growth of plants in 
saline soils. The osmotic pressure (OP) of solutions 
expressed in atmospheres is usually calculated from 
the freezing-point depression, in degrees C, AT, in 
accordance with the relation, OP^12.06aT — 
0.021 Af, given in the International Critical Tables. 

The relation between osmotic pressure and electrical 



SALINE AND ALKALI SOILS 



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40 



CONDUCTIVITY 



MILLIMH0S/cM.(ECxl0 3 ) AT 25° C. 



Figure J.-Concentration of single-salt solutions in percent as related to electrical conductivity. 



12 



AGRICULTURE HANDBOOK 60, U. S. DEPT. OF AGRICULTURE 



6000 



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CONDUCTIVITY 



MIL Li MHOS /CM. (ECxIO*) AT 25° C. 



Figure 4. -Concentration of saturation extracts of soils in milliequivalents per liter as related to electrical conductivity. 



SALINE AND ALKALI SOILS 



13 



conductivity (fig. 5) is useful for some agricultural 
purposes. This measurement is in general use and can 
be more readily measured than freezing-point depres- 
sion. The relation between OP and EC for salt mixtures 
found in saline soils is indicated in figure 6 from data 
reported by Campbell and coworkers (1949). The OP 
values were calculated from freezing-point measure- 
ments. In the range of EC that will permit plant 
growth, the relation OP^OMXEC, X10 3 can be used 
for estimating the osmotic pressure of soil solutions 
from conductivity measurements. 

Conductivity of 1: 1 and 1: 5 Extracts 

For soil: water ratios of 1: 1 and 1: 5, the extract 
is obtained by filtering without the use of vacuum or 
pressure. The conductivity of these extracts is some- 
times used for estimating salinity from the line in 
figure 4 or, preferably, from special curves that apply 
for the salts and soil in question. 

Salinity estimates based on the conductivity of 1: 1 
and 1: 5 extracts are convenient for rapid determina- 
tions, particularly if the amount of soil sample is lim- 
ited, or when repeated samplings are to be made in the 
same soil to determine the change in salinity with time 
or treatment. The rel iabi I ity -of such esti mates depends 
upon the kind of salts present. For chloride salts, the 
results will be only slightly affected by moisture con- 
tent, but, if sulfate or carbonate salts, which have 
relatively low solubility, are present in appreciable 
quantities, the apparent amount of soluble salt will de- 
pend on the soil : water ratio (table 2). In an experi- 
ment conducted by Wadleigh, Gauch, and Kolisch 
(1951) to cTetermine the salt tolerance of orchardgrass, 
the salts shown in the table were individually added 
to a loam soil. During the course of the experiment, 
many samples were taken to check distribution of the 
salt in the soil and conductivity measurements were 
made of the saturated soil (EC,), the saturation extract 
(EC,), the 1: 1 extract (EC,), and the 1: 2 extract 
(EC 2 ). Theregression coefficients, which aretheslopes 
of the best fit straight lines, were calculated for various 
comparisons among the data (table 2) . 

The theoretical values given in the table are based 
on the saturation percentage of 30 for the soil used. 
Except for small changes in the activity coefficients 
of the ions with dilution, the conductivity ratios should 



be i nversely proportional to the moisture contents of the 
soil at extraction if the total dissolved salt is inde- 
pendent of the moisture content at which the extraction 
is made. The average measured conductivity ratios 
were always greater than the theoretical. The dif- 
ferences were not large for the chloride salts, but when 
NaHC0 3 , Na 2 S0 4 , or MgS0 4 were added to this soil, 
in which the exchange complex was largely saturated 
with calcium, someCaS0 4 and CaC0 3 were precipitated. 
It is evident from the table that the regression coeffi- 
cients are quite different for extracts obtained at high 
moisture contents if the less soluble salts are present in 
the soil. This example illustrates why the estimation 
of salinity from the conductivity of the extract at 1: 1 
or at higher moisture contents is not recommended for 
general use. These higher moisture contents may be 
used to advantage in certain cases, but the limitations of 
the method should be clearly understood. 

Salinity Appraisal From the Electrical Resistance 

of Soil Paste 

Salinity determinations based on the electrical resist- 
ance of a standard sample of wet soil have been in use 
for many years (Whitney and Means, 1897; Briggs, 
1899). The Bureau of Soils cup and the data pub- 
lished by Davis and Bryan (1910) have been widely 
used by various agencies in this country for estimating 
the percentage of soluble salts in soils. The apparatus 
is simple and rugged, the measurements can be quickly 
made, and the results are reproducible. 

To obtain the relation between wet-soil resistance 
and percent salt, Davis and Bryan made measurements 
using 4 soil samples representing the textural groups 
of sand, loam, clay loam, and clay. These samples of 
soil were composited from various types of nonsaline 
soils. A mixture of chloride and sulfate salts was used 
to obtain 5 levels of added salt ranging from 0.2 to 
3 percent, and resistance values were obtained on the 
saturated pastes. Making use of these 20 readings on 
the synthetic soil and salt mixtures, Davis and Bryan 
used graphical interpolation to obtain the relation of 
soil-cup resistance to percent salt for mixed sulfates and 
chlorides. The Davis and Bryan procedure for the 
Bureau of Soils method of determining soluble salt in 
soil is given in Method 5. The method is also described 
in the Soil Survey Manual (1951,/?. 343). 



Table 2. -Regression coefficients (b) between various criteria for evaluating soil salinity by a conductance 

procedure 



Soils containing — 



^ECl-ECe 



hECt-ECe 



hEC2-ECi 



"£iCi - i!/Ce 



NaCl. . . . 

CaCU .... 
MgCl 2 . . . 
NaHCOs . 

Na 2 S0 4 ■ ■ ■ 
MgS0 4 . . . 

Theoretics 



0.359 ±0.0070 
.356± .011 
.376± .010 
.379=b .027 
.590± .023 
. 600± .068 



0.185 ± 0.0037 
. 191± .0028 
. 192± .0042 
. 227± -017 
.355± .010 
.471± .060 



0.514 ± 0.0069 
. 534± .0046 
. 507± .012 
.589± .011 
.600± .011 
. 780± .027 



0.235 ± 0.0066 
. 242 ± . 0078 
.237± .019 
.222=b .013 
.217± .015 
. 226 ± . 0054 



333 



. 167 



.5 



14 



AGRICULTURE HANDBOOK 60, TJ. S. DEPT. OF AGRICULTURE 



60 



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CONDUCTIVITY 



MILLlMH0S/CM.(ECxl03) AT 25° C. 



Figure 5. -Osmotic pressure of single-salt solutions as related to electrical conductivity. (Data from International Critical Tables.) 



SALINE AND ALKALI SOILS 



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CONDUCTIVITY 



WILLI MHOS/ CM. (ECxIO 3 ) AT 25° C. 



Ficcre 6.-Osmotic pressure of saturation extracts of soils as related to electrical conductivity. 



16 



AGRICULTURE HANDBOOK 60, U. S. DEPT. OF AGRICULTURE 



Table 3. — Comparison of measured and calculated values of EC, after correcting for effect of SP 



Soils from 



Lower Rio Grande Valley, Texas. 
Grand Junction district, Colorado. 
Tucumcari district, New Mexico. 
Gem County, Idaho.. 

Four Western States. 



A similar procedure was used by Davis and Bryan 
to obtain calibration data for "carbonate" salts, pre- 
sumably sodium carbonate. Tests at the Laboratory, 
however, indicate that table IV of Davis and Bryan 
for carbonate salts is unreliable and should not be used. 
The unreliability of the calibration data for these salts 
is a result of cation-exchange reactions that were not 
generally understood at the time the original work was 
done. 

The conductivity of the saturation extract (EC,) is 
recommended in this handbook as a measurement for 
general use for indicating soil salinity, but the method 
based on the soil-paste resistance (R,) is still com- 
monly used. The electrical conductivity of the soil 
paste (EC,) is related to paste resistance by the relation 
£C S = 0.25//? s , where 0.25 is the constant for the 
Bureau of Soils electrode cup. I n a study by Reitemeier 
and Wilcox (1946), it was found that the relation be- 
tween EC, and EC, is markedly influenced by variations 
in the saturation percentage, the salinity, and the con- 
ductivity of the soil minerals. From unpublished work 
at the Laboratory, Bower concluded that there is no 
easy method for simplifying the relation of EC, (or R s ) 
to EC,. He equilibrated a group of western soils with 
various concentrations of a 1: 1 mixture of sodium and 
calcium chloride and found that on the average 
EC J EC s = 5.4- 0.07 (SP). Using this average rela- 
tionship and SP values calculated from the weight of 
the soil paste as described by Wilcox (1951) , he calcu- 
lated values for EC, based on 7? s measurements. The 
degree of correspondence between measured and cal- 
culated values is indicated by the data in table 3. 

The calculated average values for EC, are somewhat 
high but are acceptable except for the soils from Gem 
County, Idaho. These soils had a low salinity level hut 
were high in exchangeable sodium. The large dis- 
crepancy here and for some other locations apparently 
is owing to conduction by the clay minerals, when they 
contain exchangeable sodium. Bower found, for ex- 
ample, that the electrical conductivity of a 5-percent 
suspension of calcium-saturated montmorillonite was 
0.072 mmhos/cm., but when saturated with sodium, 
the conductivity was 0.446 mmhos/ cm. 

No method has been found for improving the reli- 
ability of the paste- resistance method that does not de- 
stroy its simplicity. The method may be acceptable 



Number 

of 
samples 



6 
12 

II 

7 
12 



Average 

al 2^ 


EC, X 10 s 

i° C. 


Difference 


Standard 

deviation 

Of 

differences 


Measured 


Calculated 




9.93 


11.10 


1. 17 


1.30 


8.64 


9.45 


.81 


.85 


9.63 


11.85 


2.22 


1.16 


5.73 


16.24 


10.51 


2.90 


10.25 


13.05 


2.80 


1.76 



for estimating salinity for purposes of soil classification, 
but for soils like those of Gem County, Idaho, it does 
not have acceptable reliability. 

Conversion of Conductivity Data to a Standard 

Reference Temperature 

The electrical conductivity of solutions and of soils 
containing moisture increases approximately 2 percent 
per degree centigrade increase in temperature. To 
simplify the interpretation of salinity data, it is cus- 
tomary either to take the measurements at a standard- 
reference temperature or to determine the temperature 
at which the measurement is made, and then, by means 
of correction tables or a correction dial on the bridge, to 
convert the measurement to a standard-reference tem- 
perature. 

Whitney and Briggs (1897) measured the resist- 
ance of 9 soils at 13 temperatures and calculated the 
average rel ati on of resi stance to temperatu re. W h i tney 
and Means (1897) used these temperature data to con- 
struct a table used in converting resistance measure- 
ments of saturated soil to the standard temperature of 
60" F. Data from this table, which has been widely 
used since its publication 50 years ago, are given in 
table 16 in chapter 6, along with instructions for its use. 

M ore recently a study was made by Campbell, Bower, 
and Richards (1949) to determine the effect of tempera- 
ture on the electrical conductivity of soil extracts. 
Saturation extracts from 21 soils were measured at 5 
temperatures, ranging from 0" to 50" C. The tempera- 
ture coefficient of the electrical conductivity for these 
representative soil extracts varied somewhat with tem- 
perature, but in the range from 15" to 35" it was veri- 
fied that for each degree centigrade increase in tem- 
perature the conductivity increased very nearly 2 per- 
cent of the value at 25". The details of the procedures 
for measuring electrical conductivity and making tem- 
perature corrections are given in Method 4. 

Comparison of Percent Salt in Soil and Extract 

Measurements 

The diagram shown in figure 7 facilitates the inter- 
pretation of salinity in relation to crop response. It is 
based on the following assumptions: P sw = p. p. m,/ 
10,000-0.064X J £:CX10 3 ;P SS -(P 8W X J P W )/100; OP 



SALINE AND ALKALI SOILS 



17 



OSMOTIC PRESSURE OF SATURATION EXTRACT - ATMOSPHERES 

1.44 2.88 5.76 




2 4 6 8 10 12 14 16 

CONDUCTIVITY OF SATURATION EXTRACT — MILLIMHOS/CM. 



B 



PLANT RESPONSE 

Figure 7.-Relation of the percent salt in the soil to the osmotic pressure and electrical conductivity of the saturation extract and to 
crop response in the conductivity ranges designated by letters. These ranges are related to crop response by the salinity scale 
on page 9. 



= 0.36 X EC X 10". P sw = percent salt in water; P ss = 
percent salt in soil; P w = percent water in soil ; and 
0P= osmotic pressure in atmospheres. The lower scale 
gives values for the conductivity of the saturation ex- 
tract. The top scale shows the osmotic pressure of the 
saturation extract. The osmotic pressure of the soil 
solution at the upper limit of the field -moisture range 
will be approximately double these values. 

The diagonal lines help correlate the conductivity 
of the saturation extract with the percent salt content 
for various soil textures. For example, at EC, X 10 3 = 4, 
nearly all crops make good growth and for a soil with 
a saturation percentage of 75, as seen in the diagram, 
this corresponds to a salt content of about 0.2 percent. 
On the other hand, 0.2 percent salt in a sandy soil for 
which the saturation percentage is 25 would correspond 
to EC, X 10 3 = 12, which is too saline for good growth 
of most crop plants. Partial lists of crop plants in 
their order of tolerance to soil salinity are given in 
chapter 4. 

Thediagram indicates the growth conditions of crops 



to be expected for various degrees of salinity in the 
active root zone of the soil, i. e., the soil volume that is 
permeated by roots and in which moisture absorption 
is appreciable. Obviously, the diagram does not apply 
for soil in which salt has been deposited after the roots 
have been established and have become nonabsorbing, 
or to soil adjacent to the plant, either high or low in 
salt, that has not been permeated by roots. With ma- 
ture row crops, for example, salt may have accumulated 
in the ridge to such an extent that the roots no longer 
function as moisture absorbers and, therefore, the ridge 
cannot be considered as characteristic of the active 
plant-root environment. 

C hemi cal Deter mi nati ons 

Soil Reaction — pH 

ThepH value of an aqueous solution is the negative 
logarithm of the hydrogen-ion activity. The value may 
be determined potentiometrically, using various elec- 
trodes (Method 21), orcolorimetrically, by indicators 



18 



AGRICULTURE HANDBOOK 6 0, U. S. DEPT. OF AGRICULTURE 



whose colors vary with the hydrogen-ion activity. 
There is some question as to the exact property being 
measured when methods for determining the pH values 
of solutions are applied to soil-water systems. Appar- 
ent pH values are obtained, however, that depend on 
the characteristics of the soil, the concentration of dis- 
solved carbon dioxide, and the moisture content at 
which the reading is made. Soil characteristics that 
are known to influence pH readings include: the com- 
position of the exchangeable cations, the nature of the 
cation-exchange materials, the composition and con- 
centration of soluble salts, and the presence or absence 
of gypsum and alkaline-earth carbonates. 

A statistical study of the relation of pH readings to 
the exchangeable-sodium-percentages of soils of arid 
regions has been made by Fireman and Wadleigh 
(1951). The effect of various factors such as moisture 
content, salinity level, and presence or absence of 
alkaline-earth carbonates and gypsum upon this rela- 
tionship was also studied. Some of the more pertinent 
statistical data obtained are presented in table 4. While 
all the coefficients of correlation given in the table are 
highly significant, the coefficients of determination 
show that at best no more than 54 percent of the vari- 
ance in exchangeable-sodium-percentage is associated 
with the variance in pH reading. The data on the effect 
of moisture content indicate that the reliability of pre- 
diction of the exchangeable-sodium-percentage from pH 
readings decreases as the moisture content is increased. 
Similarly, the data on the effect of salinity indicate that 
the reliability of prediction is lowest when the salt level 
is either low or very high. An increase in pH reading 
of 1.0 or more, as the moisture content is changed from 
a low to a high value, has been found useful in some 
areas for detecting saline-alkali soils. However, the 
reliability of this procedure should be tested before use 
on any given group of soil samples. 



Experience and the statistical study of Fireman and 
Wadleigh permit the following general statements re- 
garding the interpretation of pH readings of saturated 
soil paste: (1) pH values of 8.5 or greater almost in- 
variably indicate an exchangeable-sodium-percentage 
of 15 or more and the presence of alkaline-earth carbo- 
nates; (2) the exchangeable-sodium-percentage of soils 
havi ng pH val ues of less than 8.5 may or may not exceed 
15; (3) soils having pH values of less than 7.5 almost 
always contain no alkaline-earth carbonates and those 
having values of less than 7.0 contain significant 
amounts of exchangeable hydrogen. 

Soluble Cations and Anions 

Analyses of saline and alkali soils for soluble cations 
and anions are usually made to determine the compo- 
sition of the salts present. Complete analyses for sol- 
uble ions provide an accurate determination of total salt 
content. Determinations of soluble cations are used to 
obtain the relations between total cation concentration 
and other properties of saline solutions, such as electri- 
cal conductivity and osmotic pressure. The relative 
concentrations of the various cations in soil-water ex- 
tracts also give information on the composition of the 
exchangeable cations in the soil. 

The soluble cations and anions commonly deter- 
mined in saline and alkali soils are calcium, magnesium, 
sodium, potassium, carbonate, bicarbonate, sulfate, and 
chloride. Occasionally nitrate and soluble silicate also 
are determined. In making complete analyses, a de- 
termination of nitrate is indicated if the sum of cations 
expressed on an equivalent basis significantly exceeds 
that of the commonly determined anions. Appreciable 
amounts of soluble silicate occur only in alkali soils 
having high pH values. In analyses made by the usual 
methods, including those recommended in this hand- 



Table4. — Coefficient of correlation (r) 1 and coefficient of determination (r 2 ) for the relation of pH reading to 
exchangeable-sodium.-percentage as influenced by moisture content, salinity level, and presence or absence of 
alkaline-earth carbonates and gypsum 



M oisture 

content 

(percent) 


Salinity as 
EC, x 10 3 

at 25° C. 


Alkaline- 
earth 
carbonates 


Gypsum 


Samples 


r 


r 2 


Saturation 


Variable 

... .do 

.... do 

o-4 

4-8 

8-15 


Variable. 

do 

do 

d o 

do 

do 

do 

do. 

do 

Present. 

Absent . 


Variable. 

.do. 
d o 
do 

do 

do 

do : 

do 

do. 

Present 
Absent, 
do 


Number 
868 
271 
289 
346 

349 

91 

115 

87 

69 

237 
452 
154 


0.66 

.65 
.53 
.48 

.56 

.72 

.70 

74 

:49 

.72 
.56 
.41 


Percent 
44 


500 

1,000 


43 

28 


6,000 


24 


Saturation. 

D o 
D o 


31 
52 
49 


D o 


15-30 


54 


D o 


> 30 


24 


Do. 


Variable 


52 


Do. 

Do. 


... do 


32 
17 



1 All values are significant at the 1-percent level. 



SALINE AND ALKALI SOILS 



19 



book, any soluble silicate present is determined as 
carbonate. 

As shown by Reitemeier (1946) and others, values 
obtained from determinations of the soluble-cation and 
soluble-anion contents of saline and alkali soils are 
markedly influenced by the moisture content at which 
the extraction is made. The total dissolved quantities 
of some ions increase with increasing moisture content, 
while concurrently those of others may decrease; al- 
most invariably values obtained for total salt content 
increase with increasing moisture content at extraction. 
Processes that are responsible for the changes in the 
relative and total amounts of soluble ions which occur 
with increasing moisture content include cation-ex- 
change reactions, negative adsorption of ions, hydrol- 
ysis, and the increased solution of silicate minerals, 
alkaline-earth carbonates, and gypsum. Ideally, the 
determination of soluble ions should be made on ex- 
tracts obtained at a moisture content in the field- 
moisture range. However, the preparation of such 
extracts is time-consuming and requires the use of 
special extraction equipment (Method 3d). Saturation 
percentage is the lowest practical moisture content for 
obtaining extracts on a routine basis. Use of the 
saturation extract is, therefore, recommended for the 
determination of soluble ions. Methods are available 
that permit determination of the electrical conductivity 
and the common soluble constituents on 10 to 50 ml. 
of saturation extract. As a rule, about one-fourth of 
the moisture in a saturated soil paste can be removed 
by ordinary pressure or vacuum filtration. 

The choice of methods for the determination of the 
various cations and anions depends upon the equip- 
ment available and the personal preference of the 
analyst. No attempt is made here to present all of the 
methods that are suitable. The methods given were 
chosen on the basis of their convenience and reliability. 
Owing to the fact that the amount of extract available 
for analysis is usually limited, most of the methods 
selected are of the semi micro type. They generally in- 
volve the use of a centrifuge, a flame photometer, and a 
photoelectric colorimeter. Where the amount of ex- 
tract is not limited, the macromethods employed for 
water analysis given i n chapter 8 may be used . M ost of 
these methods do not require the use of a centrifuge or 
photoelectric colorimeter. 

Soluble Boron 

The importance of soluble boron from the standpoint 
of soil salinity lies in its marked toxicity to plants when 
present in relatively small amounts. Toxic concentra- 
tions of boron have been found in the saturation ex- 
tracts of a number of saline soils. It is necessary, 
therefore, to consider this constituent as a factor in the 
diagnosis and reclamation of saline and alkali soils. 
High levels of boron in soils can usually be reduced by 
leaching. During the leaching process, boron may not 
be removed in the same proportion as other salts. If the 
concentration of boron is high at the outset, a consider- 
able depth of leaching water may be necessary to reduce 



the boron content to a safe value for good plant growth. 
This is illustrated by a recent leaching test. At the 
beginning of the test, the conductivity of the saturation 
extract of the top 12 inches of soil was 64.0 mmhos/ cm. 
After 4 feet of irrigation water had passed through the 
soil, the conductivity was reduced to 4.2 mmhos/cm.; 
after 8 feet, the conductivity was 3.4 mmhos/cm.; and 
after 12 feet, it was 3.3 mmhos/cm. The concentration 
of boron in the saturation extract at the start of the test 
was 54 p. p. m. After the passage of 4 feet of water, 
the concentration was 6.9 p. p. m.; after 8 feet, it was 
2.4 p. p. m.; and after 12 feet, it was 1.8 p. p. m. Thus, 
leaching with 4 feet of water reduced the salinity to a 
safe level, but the boron content was still too high for 
good growth of plants sensitive to boron. 

Permissible limits for boron in the saturation extract 
of soils can at present be given only on a tentative basis. 
Concentrations below 0.7 p. p. m. boron probably are 
safe for sensitive plants (ch. 4) ; from 0.7 to 1.5 p. p. m. 
boron is marginal; and more than 1.5 p. p. m. boron 
appears to be unsafe. The more tolerant plants can 
withstand higher concentrations, but limits cannot be 
set on the basis of present information. For land on 
which crops are being grown, a better appraisal of 
boron conditions often can be made by an analysis of 
plant samples (ch. 4) than can be obtained from an 
analysis of soil samples. 

Exchangeable Cations 

When a sample of soil is placed in a solution of a 
salt, such as ammonium acetate, ammonium ions are 
adsorbed by the soil and an equivalent amount of 
cations is displaced from the soil into the solution. 
This reaction is termed "cation exchange," and the 
cations displaced from the soil are referred to as "ex- 
changeable." The surface-active constituents of soils 
that have cation-exchange properties are collectively 
termed the "exchange complex" and consist for the most 
part of various clay minerals and organic matter. The 
total amount of exchangeable cations that a soil can 
retain is designated the "cation-exchange-capacity," and 
is usually expressed in milliequivalents per 100 gm. of 
soil. It is often convenient to express the relative 
amounts of various exchangeable cations present in a 
soil as a percentage of the cation-exchange-capacity. 
For example, the exchangeable-sodium-percentage 
(ESP) is equal to 100 times the exchangeable-sodium 
content divided by the cation-exchange-capacity, both 
expressed in the same units. 

Determinations of the amounts and proportions of 
the various exchangeable cations present in soils are 
useful, because exchangeable cations markedly influ- 
ence the physical and chemical properties of soils. The 
exchangeable-cation analysis of saline and alkali soils 
is subject to difficulties not ordinarily encountered with 
other soils, such as those from humid regions. Saline 
and alkali soils commonly contain alkaline-earth carbo- 
nates and a relatively high concentration of soluble 
salts. They may have low permeability to aqueous 
solutions and to alcohol. Solutions capable of displac- 



20 



AGRICULTURE HANDBOOK 60, U. S. DEPT. OF AGRICULTURE 



ing exchangeable cations from soils dissolye most or all 
of the soluble salts and significant amounts of the carbo- 
nates of calcium and magnesium if they are present. 
The soluble salts should not be washed out of the soil 
prior to extracting the exchangeable cations, because of 
significant changes that take place as a result of dilution 
and hydrolysis. The dissolving of salts, therefore, 
necessitates independent determinations of soluble- 
cation contents and correction of the exchangeable- 
cation analysis for their presence, while the occurrence 
of calcium and magnesium carbonates prevents accurate 
determination of exchangeable calcium and magnesium. 
Furthermore, the low permeability of many alkali soils 
renders the conventional leaching techniques for dis- 
placement of cations time-consuming and inconvenient. 

Neutral normal ammonium acetate is the salt solution 
most commonly used for the extraction of exchangeable 
cations and for the saturation of the exchange complex 
in the determination of cation-exchange-capacity. Al- 
though this solution has many advantages for exchange- 
able-cation analysis, some saline and alkali soils fix ap- 
preciable amounts of ammonium as well as potassium 
ions under moist conditions. The fixation of ammo- 
nium does not interfere with the extraction of exchange- 
able cations, but values obtained for cation-exchange- 
capacity by ammonium saturation are low by amounts 
equal to the quantity of ammonium fixed. The desir- 
ability of using a cation not subject to fixation for the 
determination of cation-exchange-capacity is, therefore, 
evident. 

As discussed in a previous section, the determined 
values for the soluble-ion contents of soils vary with 
the moisture content at which the extraction is made, 
because equilibria exist between the soluble and ex- 
changeable cations in soils, the changes in relative and 
total concentrations of soluble cations with variations 
in moisture content are accompanied by changes in the 
relative composition of the exchangeable cations. In 
a strict sense, therefore, values for exchangeable-cation 
contents apply only at the moisture content used for the 
extraction of soluble cations. Owing to difficulties in- 
volved in the determination of soluble cations at mois- 
ture contents in the field range, it is convenient to deter- 
mine exchangeable-cation contents at the saturation 
percentage. 

Consideration of the various factors involved in the 
determination of the exchangeable cations and the 
cation-exchange-capacity of saline and alkali soils has 
led to the adoption of the following scheme of 
analysis: 

(a) Extract a sample of the soil with an excess of 
neutral normal ammonium acetate solution and deter- 
mine the mill iequivalents of the various cations removed 
per 100 gm. of soil. 4 

(b) Prepare a saturation extract of the soil and de- 
termine the mi 1 1 iequivalents of the various soluble 
cations per 100 gm. of soil." 

(c) Calculate the exchangeable-cation contents of 
the soil by subtracting the amounts of the various cat- 
ions dissolved in the saturation extract from the 



amounts extracted by the ammonium acetate solution. 

(d) Determine the cation-exchange-capacity by 
measuring the mi 1 1 iequivalents of sodium adsorbed per 
100 gm. of soil upon treating a sample with an excess 
of normal sodium acetate solution of pH 8.2. 

The difficulties encountered in leaching soil samples 
of low permeability are overcome by shaking and 
centrifuging samples in centrifuge tubes with successive 
portions of the extraction and wash liquids. Neutral 
normal ammonium acetate solution is used for the ex- 
traction of exchangeable plus soluble cations, because 
its interference in analytical procedures is easily elimi- 
nated. Of the common cations, sodium appears to be 
the most suitable for determining cation-exchange- 
capacity. As mentioned previously, ammonium and 
potassium are subject to fixation in difficultly exchange- 
able form and the usual presence of calcium and mag- 
nesium carbonates in saline and alkali soils precludes 
the use of extractants containing calcium or magnesium. 
The fact that sodium is a prominent cation in most 
saline and alkali soils also favors its use in the determi- 
nation of cation-exchange-capacity (Method 19). 

Gypsum 

Gypsum is found in many soils of arid regions, in 
amounts ranging from traces to several percent. In 
some soils, gypsum was present in the sedimentary de- 
posits from which the soil was derived; whereas, in 
other soils the gypsum was formed by the precipitation 
of calcium and sulfate during salinization. Owing to 
leaching, gypsum commonly occurs at some depth in the 
former instance, while in the latter its content is 
usually greatest in the surface layers of the soil. 

Information regarding the gypsum content of alkali 
soils is important, because it usually determines whether 
the application of chemical amendments will be re- 
quired for reclamation. Also, the presence of con- 
siderable amounts of gypsum in the soil might permit 
the use of an irrigation water having an unfavorably 
high sodium content. 

The precise determination of gypsum in soils is 
difficult, because of inherent errors involved in the 
extraction of this mineral by water. Studies by Reite- 
meier (1946) and others show that at least three factors 
other than the solution of gypsum may influence the 
amounts of calcium and sulfate extracted from gypsif- 
erous soils. They are: (1) The solution of calcium 
from sources other than gypsum ; (2) exchange reac- 
tions in which soluble calcium replaces other cations, 
such as sodium and magnesium; and (3) the solution 
of sulfate from sources other than gypsum. 



4 If the soil is known to contain carbonates of calcium and 
magnesium, determination of these cations is omitted. Like- 
wise, if the soil is known to Contain gypsum not completely 
soluble in the saturation extract, the determination of calcium 
is omitted. In the absence of prior knowledge regarding the 
calcium and magnesium carbonate and gypsum contents of the 
soil, the calcium and magnesium determinations are disregarded 
if upon completion of the exchangeable-cation analysis the sum 
of the values obtained for exchangeable-cation contents is found 
to exceed the cation-exchange-capacity value. 



SALINE AND ALKALI SOILS 



21 



Three methods are given in chapter 6 for the esti- 
mation of gypsum in soils. Methods 22a and 22b are 
based on the low solubility of the salt in an aqueous 
solution of acetone. Method 22a is essentially quali- 
tative, although a rough estimate of gypsum content 
may be obtained by visual observation of the amount 
of precipitate obtained. This method can be success- 
fully employed under field conditions. In Method 22b 
the separated and washed gypsum precipitate is deter- 
mined quantitatively. The use of Method 22c is ad- 
vantageous when characterization of the soil includes 
the determination of calcium plus magnesium in the 
saturation extract. It is based on the increase in 
soluble-divalent-cation content as the moisture content 
of the soil is increased from the saturation percentage 
to a moisture content sufficient to dissolve the gypsum 
present. It should be noted that this method can give 
negative values for gypsum content as a result of the 
replacement of exchangeable sodium and potassium by 
calcium as the moisture content of the soil is increased. 
This is likely to occur only in alkali soils containing 
little or no gypsum. 

Alkaline-Earth Carbonates (Lime) 

The alkaline-earth carbonates that occur in signifi- 
cant amounts in soils consist of calcite, dolomite, and 
possibly magnesite. Owing to low rainfall and limited 
leaching, alkaline-earth carbonates are usually a con- 
stituent of soils of arid regions. The amounts present 
vary from traces to more than 50 percent of the soil 
mass. Alkaline-earth carbonates influence the texture 
of the soil when present in appreciable amounts, for 
the particles commonly occur in the silt-size fraction. 
The presence of fine alkaline-earth carbonate particles 
is thought to improve the physical condition of soils. 
Conversely, when alkaline-earth carbonates occur as 
caliche or as cementing agents in indurated layers, the 
movement of water and the development of root systems 
is impeded. Alkaline-earth carbonates are important 
constituents of alkali soils, for they constitute a poten- 
tial source of soluble calcium and magnesium for the 
replacement of exchangeable sodium. As discussed in 
another section, the choice of chemical amendments 
for the replacement of exchangeable sodium is directly 
related to the presence or absence of alkaline-earth 
carbonates. 

Effervescence upon application of acid (Method 23a) 
can be used to detect as little as 0.5 percent of alkaline- 
earth carbonates in soils. This test suffices for most 
purposes. When a better esti mate of the alkaline-earth- 
carbonate content of soils is desired, Methods 23b or 
23c may be used. A quantitative determination of 
small amounts of alkaline-earth carbonates in soils is 
sometimes desirable in connection with proposed appli- 
cations of acid-forming amendments. For precise de- 
terminations, the reader is referred to the methods of 
Williams (1949) and Schollenberger (1945). 



Physical Determinations 

The problem of evaluating soil physical conditions 
has recently been separated into components by the 
American Society of Agronomy (1952) ; and they are 
discussed under the headings of mechanical impedance, 
aeration, soil water, and soil temperature. These are 
logical ultimate aspects; but, for practical work on 
alkali soils, measuring methods are needed that yield 
immediate results having more or less direct diagnostic 
significance. Some progress is being made toward 
evaluating the physical status of soil in terms of physi- 
cal properties, i. e., intrinsic qualities of soil that can 
be expressed in standard units and that have values 
which are substantially independent of the method of 
measurement. Infiltration rate, permeability, bulk 
density, pore-size distribution, aggregation, and modu- 
lus of rupture appear to be such properties. Experi- 
ence indicates that the physical status of any given soil 
is not static. There is a range of variation of physical 
status that is related to productivity, and this is re- 
flected in corresponding ranges in the values of per- 
tinent physical properties. 

Information on the existing physical status of a 
problem soil is useful for purposes of diagnosis or 
improvement, but it might also be useful to know how 
much better or worse the status can be made by chemi- 
cal and physical treatments simulating those applicable 
under field conditions. Soils can be treated to increase 
the exchangeable-sodium-percentage and then puddled 
to indicate how unfavorable the physical status can be 
made. It should also be possible by use of soil amend- 
ments and chemical aggregants to get some indication 
of how favorable the physical status can be made. 
Practical use of the concept that there is a range of 
physical states for any given soil may have to wait for 
refinements in measuring methods, but the idea seems 
to be pertinent to the improvement of alkali soils. 

Infiltration Rate 

Water-movement rates attainable in soil under field 
conditions relate directly to irrigation, leaching, and 
drainage of saline and alkali soils. Infiltration refers 
to the downward entry of water into soils and the term 
"infiltration rate" has special technical significance in 
soils work. Definitions of soil-water terms adopted by 
the Soil Science Society of America (1952) are fol- 
lowed, and are included in the Glossary. 

The infiltration rate of soil is influenced by such 
factors as the condition of the soil surface, the chemical 
and physical status and nature of the soil profile, and 
the distribution of water in the profile. All of these 
factors change more or less with time during infil- 
tration. 

The infiltration rate is measured under field condi- 
tions. The principal methods used have involved flood- 
ing or impounding water on the soil surface, sprinkling 
to simulate rain, and measuring water entry from rills 
or furrows. In addition to the multitude of local 
physical conditions that are encountered in the field, 



22 



AGRICULTURE HANDBOOK 60, U. S. DEPT. OF AGRICULTURE 



the availability of equipment, materials, and services 
will largely decide what method to use in measuring in- 
filtration. Although many measurements have been 
made, as evidenced by the extensive bibliography of 
Davidson (1940) , there does not seem to be a generally 
accepted procedure applicable to all situations. Many 
of the infiltration measurements made by this Labora- 
tory have been in connection with basin irrigation on 
test plots ranging from 10 to 20 feet square. The 
water-subsidence rate in a large plot is probably the 
best indication of the infiltration rate as related to 
leaching operations, but this method is usually not 
feasible for exploratory or diagnostic measurements in 
new areas. The cylinder method of Musgrave (1935) is 
probably the most versatile of the various methods 
available. A guard ring is needed if lateral spreading 
is excessive. Procedures for making infiltration meas- 
urements are given in Method 28. 

Water having the same quality as that which will be 
used for irrigation or leaching must be used for infil- 
tration tests in the field, otherwise the results may be 
misleading. Thelength of time the tests should becon- 
ducted and the depth of water to be applied depend 
upon the purpose of the test and the ki nd of i nformation 
that is sought. If it is a matter of appraising an irriga- 
tion problem, the depth corresponding to one irrigation 
may be sufficient; but, if information on infiltration for 
planning a leaching operation is needed, it may be de- 
sirable to apply the full depth of leaching water to a 
test plot. It often happens that subsurface drainage is 
sufficiently restricted to cause the infiltration rate to 
decrease considerably with time. It should be kept in 
mind, therefore, that although small area tests will give 
useful information on soil changes during leaching, the 
infiltration values thus obtained will apply to large areas 
only if underdrainage is not limiting. 

Experience indicates that the infiltration rate of a 
given soil can be high or low, depending on physical 
status and management history. Infiltration rate is 
often critically influenced by surface soil conditions, 
but subsurface layers also are sometimes limiting. 
Water distribution in the profile and depth of water 
applied are modifying factors. The infiltration rate 
can be undesirably high or undesirably low. It is the 
low end of the range that may be a critical limiting 
factor in the agricultural use of alkali soils. It is diffi- 
cult to specify a boundary limit between satisfactory 
and unsatisfactory infiltration rates at the low end of 
the range, because so many factors are involved, in- 
cluding the patience and skill of the farmer. However, 
if the infiltration rate is less than 0.25 cm./hr. (0.1 
in./hr.) special water- management problems are in- 
volved that may make an irrigation enterprise 
unprofitable for average operators. 

Permeability and Hydraulic Conductivity 

The permeability of soil, in a qualitative sense, refers 
to the readiness with which the soil conducts or trans- 
mits fluids. In a quantitative sense, when permeability 
is expressed with numbers, it seems desirable that per- 



meability be defined as a property of the porous medium 
alone and independent of the fluid used in its measure- 
ment. The term "hydraulic conductivity," on the other 
hand, is used to refer to the proportionality factor in 
the Darcy flow equation. These distinctions represent 
increased specialization in the use of these terms as ap- 
proved by the Soil Science Society of America ( 1952). 
No change in the qualitative use of the word "permea- 
bility" is involved. In the quantitative sense, involving 
numerical values, the term "intrinsic permeability" 
will mostly be used and will refer to a length-squared 
measurement that may be identified in a general way 
to the cross-sectional area of some equivalent or effec- 
tive size of pore. 

An immediate consequence of this clarification of 
nomenclature is a new method for evaluating pore-space 
stability or structural stability of soil. For porous 
media with fixed structure, such as sandstone or fired 
ceramic, measurements of intrinsic permeability with 
air, water, or organic liquids all give very nearly the 
same numerical value. Gravity, density, and the vis- 
cosity of the liquid are taken into account in the flow 
equation. However, if the intrinsic permeability for 
a soil as measured with air is markedly greater than the 
permeability of the same sample as subsequently meas- 
ured using water, then it may be concluded that the 
action of water in the soil brings about a change in 
structure indicated by the change in permeability. The 
ratio of air to water permeability, therefore, is a meas- 
ure of the structural stability of soils, a high ratio 
indicating low stability. 

Intrinsic-permeability measurements are based on 
the equation v=^k'dgi/-q, where v is the flow velocity, 
k' is the intrinsic permeability, d is the density of the 
fluid, g is the acceleration of gravity, i the hydraulic 
gradient, and -q is the viscosity. Procedures for measur- 
ing intrinsic permeability with gases and liquids are 
given as Methods 37a and 37b. The air-water per- 
meability ratio increases greatly as the exchangeable- 
sodium content of the soil increases, indicating that 
exchangeable sodium decreased the water stability of 
the soil structure. 

It is seen from the Darcy equation, v~ki, that k, 
the hydraulic conductivity, is the effective flow velocity 
or discharge velocity of water in soil at unit hydraulic 
gradient, i. e., when the driving force is equal to 1 
gravity. Methods 34a and 34b give procedures for 
measuring hydraulic conductivity on undisturbed and 
disturbed soil samples. 

Under some circumstances, especially when the soil 
surface has been subject to submergence by water for 
a considerable period and when the hydraulic con- 
ductivity is nearly uniform with depth, the hydraulic 
gradient beneath the soil surface may approach unity, 
i. e., the downward driving force is composed entirely 
of the gravity force with no pressure gradient. U nder 
this condition the infiltration rate is equal to the hy- 
draulic conductivity, but this is probably the exception 
rather than the rule under field conditions. Conse- 
quently, the relation between infiltration rate and 
hydraulic conductivity is not a simple one. For ex- 



SALINE AND ALKALI SOILS 



23 



ample, at the Malheur Experimental Area in Oregon, 
very low hydraulic-conductivity values were obtained 
and yet infiltration was adequate to support good crops 
with sprinkler irrigation. It was found by use of 
tensiometers that values for the hydraulic gradient 
during infiltration ranged up to 10 in some cases. This 
soil was deep and silty and the suction gradient in the 
soil added significantly to the rate of downward move- 
ment of water. If the downward flow is interrupted 
by a layer of very low conductivity, then the hydraulic 
gradient may approach zero as the soil pores become 
filled and the condition of static equilibrium under 
gravity is approached. 

It is to be expected that if the hydraulic conductivity 
of surface soil is as low as 0.1 cm./hr. (0.04 in. /hr.) 
leaching and irrigation may present serious difficulties. 
Irrigation agriculture under average conditions of 
management skill, water quality, and drainage condi- 
tions would have doubtful success unless the hydraulic 
conductivity could be increased appreciably by soil- 
improvement measures. 

Moisture Retention by Soil 

The effect of soil salinity on crops is related to the 
range over which the moisture content of the soil varies, 
because the concentration of the soil solution depends 
both on the amount of soluble salt and the amount of 
water present. The permanent-wilting percentage, as 
indicated in the review by Veihmeyer and Hendrickson 
(1948), is generally accepted as being the lower limit 
of water available for plant growth in nonsaline soil. 
For all practical purposes, the 15-atmosphere percent- 
age (Method 31) can be used as an index of the 
permanent-wilting percentage and, therefore, also as 
an acceptable index of the lower limit of the available 
range of soil moisture. This lower limit appears to be 
an intrinsic property of the soil that is largely deter- 
mined by soil texture and appears to be substantially 
independent of the kind of plant grown on the soil. 

It is much more difficult to set an upper limit for 
the range of water content available to plants in the 
field. In addition to dependence upon soil texture at 
the point in question, the upper limit depends also on 
the variation throughout the profile of such factors as 
pore-size distribution and water conductivity. The dis- 
tribution of water with depth influences the hydraulic 
gradient, and, therefore, also the rate of downward 
movement of water. For example, with or without 
active roots, the moisture content in the surface layers 
of a deep permeable soil will decrease more slowly if 
the profile is deeply wetted than if only a shallow depth 
is wetted and the underlying soil isdry. Also, thetotal 
amount of water actually availablefrom any given layer 
of surface soil depends on the rooting depth and trans- 
piration rate of the crop. The hydraulic boundary con- 
ditions that characterize the field situation would be 
extremely difficult to reproduce for a soil sample re- 
moved from the profile, and it is not surprising that no 
generally satisfactory laboratory method has been 
found for estimating the upper limit of water available 



for crop growth under field conditions. A field de- 
termination under representative field conditions is the 
best method for obtaining the upper limit of the field- 
moisture range. 

For most medium- to fine-textured soils, the upper 
limit of available water is approximately twice the 
moisture percentage of the lower limit. This does not 
hold true for the coarse- textured soils. It has been 
found by the United States Bureau of Reclamation 
(1948) that for the sandy soils occurring on the Yuma 
Mesa, Arizona, the water retained in a sample of soil 
at the y 10 -atmospheTe percentage (Method 29) satis- 
factorily approximates the upper limit of available 
water under field conditions. 

Density and Porosity 

The bulk density (apparent density) of soil is the 
mass of soil per unit volume, and the porosity of soil 
is the fraction of the soil volume not occupied by soil 
particles. Bodman (1942) has discussed soil density 
in connection with water content and porosity relation- 
ships and has prepared useful nomograms (fig. 8). 

The bulk density of soil can be measured by several 
methods. For a certain range of moisture contents with 
soils that are comparatively free of gravel and stones, 
it is possible to press into the soil a thin-walled tube 
having a suitable cutting edge. The soil is then 
smoothed at each end of the tube and oven-dried at 
105" C. The bulk density is the mass of soil contained 
in the tube divided by the volume of the tube, as indi- 
cated i n M ethod 38. 

The porosity of soil (n) may be obtained directly 
from air-pycnometer measurements or can be calcu- 
lated from the relation n = (d p — d h )/d p , where d p is the 
average density of the soil particles and d h is the bulk 
density. 

The particle density of many soils averages around 
2.65 gm. cm.?. The average particle density for peat 
soils or for pumice soils is much lower. Direct meas- 
urements of particle density can be made with pycnom- 
eter bottles (Method 39). 

The bulk density of most soils ranges from 1.0 gm. 
cm.? for clays, to 1.8 gm. cm.? for sands. This corre- 
sponds to the range of 62.4 to 112 lb. ft.?. The corre- 
sponding porosity range will be from about 0.60 to 0.30. 
Bulk density may become a critical factor in the pro- 
ductivity of soil. Veihmeyer and Hendrickson (1946) 
found that plant roots were unable to penetrate a 
gravelly loam soil when the bulk density exceeded a 
value of around 1.8 gm. cm.?. Also, when the bulk 
density of medium- to fine-textured subsoils exceeds 
about 1.7 gm. cm; 3 , hydraulic conductivity values will 
be so low that drainage d iff icu I ties can be anticipated. 

Aggregation and Stability of Structure 

The arrangement of soil particles into crumbs or ag- 
gregates that are more or less water stable is an im- 
portant aspect of soil structure. Alkali soils often 
have a dense, blocky, single-grain structure, are hard to 
till when dry, and have low hydraulic conductivity when 



WATER 
CONTENT 

PERCENT 
50 - 



40 



30 



20 



t 



!0 - 

9 ^t 
8 

7 

6 -- 

5 -- 

- : 
-- 

4 -- 



3 -- 



2 -- 



DEPTH OF WATER 

PER FOOT OF SOIL 

INCHES FEET 

12 - 

II - 



10 ^ 

9 -| 

8 -E 

7 - 



5 — 
4 



1.00 
.90 

-80 
70 

60 
SO 

.40 



; - .30 



.20 



2 — 



0.4 - 



0.3 - 





H- .10 


J 


k 


- 


- .09 


1 — 


■ 




- .08 


OS E 






1" ° 7 


0.8 - 




CD.7 -E 


- .06 


©.6 i 


05 


05 - 





-- .04 



— 03 



.02 



0.2 



- .01 



0.! J 



C, c 2 



APPARENT 

DENSITY 

GMSVCM. 3 LBS/FT* 



120 



1.9 — Z 



1.8 — 



1.7 — 



1.6 



1.5 



J. 4 



.3 — - 



12 



I.I ■ 



1.0 — 



0.9 



0.8 



110 



100 



90 



80 



70 



50 



B, 



50 



APPARENT 
DENSITY 



GMSA*I S 
2.0 -| 

1.9-1 = 



1.8-1 E 
-i — 110 



I 6 -| — 100 

1.5 -%z 

-|=- 90 
t.4- 



1.3-= 
1.2 4 

I.I - 
I. O-EI 

0.9-E 



LBS/FT' 



-120 



80 



70 



60 



0.8^- 50 

A a, 



TOTAL 
PORE SRACE 

POROSITY VOtDRATlO 
— — 



0,|-| -0.1 

1—02 
. 2: — E — 
J -0.3 

o.3-= r - 4 

^ r 05 

= -0.6 
0.4—- 

i-0.8 



0.5 — -1.0 



0.6— — 15 



0.7 



0.8- 



:e?2.o 

-i 2,5 
"i 30 

-E3.5 



-4.0 



E A L 

NSITY 

GtlS/CM 5 



B 



3.0 



to 



> 

a 

o 
d 

d 
H 

W 

td 
O 
O 

W 

OS 

o 






O 






DENSITY AND SOIL WATER 



DENSITY AND SOIL AIR SPACE 



Figure 8.-Nomograms giving soil density, soil water, and soil air space relationships (Bodman, 1942). 



SALINE AND ALKALI SOILS 



25 



wet. This is generally because the aggregates and also 
the pores of such soils are not stable. The aggregates 
slake down in water, and the pores become filled with 
fine particles. 

Several methods have been proposed for measuring 
the water stability of soil aggregates, the most common 
being the wet-sieving method proposed by Yoder 
(1936). A modification of the Yoder procedure is 
given as Method 42a. Soils that are low in organic 
matter and contain appreciable amounts of exchange- 
able sodium seldom contain aggregates of larger sizes 
and for that reason measuring procedures adapted for 
the smaller aggregates are included as Method 42b. 
This determination is related to Middleton's (1930) 
"dispersion-ratio," but M ethod 42a gives the percentage 
by weight of particles smaller than 50/x that are bound 
into water-stable aggregates greater than 50/x. Insuf- 
ficient data are available at the present time to specify 
limits that will help to distinguish between problem and 
nonproblem soils as far as aggregate-size distribution is 
concerned. 

Chi Ids (1940) followed the change in moisture-reten- 
sion curves with successive wettings to get an index of 
the stability of structure, or, more precisely, the stabil- 
ity of the pore-space arrangement. Reeve and co- 
workers (fig. 1) have shown that the ratio of the air 
permeability to the water permeability for soils is also 
a useful index of the stability of soil structure (Method 
37). 

Recent studies by Allison (1952) and by Martin 
and associates (2952) indicate that dispersed soils may 
be rapidly and effectively improved by application of 
aggregating agents of the poly electrolyte type. Ap- 
plied at the rate of 0.1 percent on the dry-soil basis, 
this material has effectively improved the physical 
condition of alkali soils on which it has been tried. 
Salinity appears to havelittleor no effect on the process. 
A higher degree of aggregation was obtained where 
the aggregating agent in solution was sprayed on dry 
soil and mixed in than when it was applied dry to a 
moist soil followed by mixing. Regardless of the man- 
ner of application, large increases in infiltration rate 
and hydraulic conductivity resulted from its use. 

Although not yet economically feasible for general 
agricultural use, aggregating agents can bean effective 
research tool for investigational work with saline and 
alkali soils. By their use, for instance, plant response 
to different levels of exchangeable sodium or different 
Ca: Na ratios may be studied on "conditioned" soils 
in the absence of poor structure and accompanying 
conditions of deficient aeration and low water-move- 
ment rates ordinarily present in alkali soils, 

It seems likely, also, that soil -aggregating chemicals 
may provide a rapid method for appraising the struc- 
tural improvement potentially attainable from organic- 
matter additions. Organic-matter additions, while 
slower to give results, have long been used in agricul- 
ture. There may be soils, such as those high in silt 
and low in clay, in which coarse organic matter may 
give improvements in physical condition that are unat- 
tainable with chemical aggregants. 

259525 0-54-3 



Crust Formation 

Soils that have low stability of structure disperse 
and slake when they are wetted by rain or irrigation 
water and may develop a hard crust as the soil surface 
dries. This crust presents a serious barrier for emerg- 
ing seedlings, and with some crops often is the main 
cause of a poor stand. Alkali soils are a special prob- 
lem in this regard, but the phenomenon is by no means 
limited to these soils. 

Factors influencing development of hard surface 
crusts appear to be high exchangeable sodium, low 
organic matter, puddling, and wetting the soil to zero 
tension, which occurs in the field with rain or irriga- 
tion. Crust prevention would, therefore, involve re- 
moval of exchangeable sodium, addition of organic 
matter, and care to avoid puddling during tillage and 
other operations. Where possible, the placement of 
the seed line somewhat above the water level in a fur- 
row is desirable so that the soil above the seed will be 
wetted with water at appreciable tensions, thus lessen- 
ing the tendency for soil aggregates at the surface to 
disintegrate. 

The procedure for measuring the modulus of rupture 
of soil (Method 43) was developed for appraising the 
hardness of soil crusts, since a satisfactory measuring 
method is essential in developing and testing soil 
treatments for lessening soil crusting. 

Choice of Determinations and 
Interpretation of Data 

Equilibrium Relations Between Soluble and 

Exchangeable Cations 

Cation exchange can be represented by equations 
similar to those employed for chemical reactions in 
solutions. For example, the reaction between calcium- 
saturated soil and sodium chloride solution may be 
written :CaX 2 + 2NaC1^2Na£ +CaCl 2 , where X desig- 
nates the soil exchange complex. As shown by the 
equation, the reaction does not go to completion, be- 
cause as long as soluble calcium exists in the solution 
phase there will be adsorbed calcium on the exchange 
complex and vice versa. Equations have been pro- 
posed by various workers for expressing the equilibrium 
distribution of pairs of cations between the exchange- 
able and soluble forms. For metallic cation pairs of 
equal valence, many of the equations assume the same 
form and give satisfactory equilibrium constants, but 
variable results are obtained with thedifferent equations 
when cations of unequal valence are involved. Accord- 
ing to the work of Krishnamoorthy and Overstreet 
(1950), an equation based on the statistical thermo- 
dynamics of Guggenheim (1945) is most satisfactory 
for cation pairs of unequal valence. All of the equa- 
tions become less satisfactory when applied to mixtures 
of cation-exchange materials having different equi- 
librium constants. 

The use of cation-exchange equations for expressing 
the relationship between soluble and exchangeable 



26 



AGRICULTURE HANDBOOK 6 0, U. S. DEPT. OF AGRICULTURE 



cations in soils of arid regions involves inherent diffi- 
culties. The difficulties arise from the presence of 
mixtures of different kinds of cation-exchange mate- 
rials in soils and from the fact that usually four cation 
species must be dealt with. Moreover, there are no 
accurate methods available for determining exchange- 
able calcium and magnesium in soils containing 
alkaline-earth carbonates and gypsum. Despite these 
difficulties, some degree of success has been attained 
in relating the relative and total concentrations of 
soluble cations in the saturation extract of soils to the 
exchangeable-cation composition, using a somewhat 
empirical approach. Direct determinations show that, 
when soils are leached with salt solutions containing 
a mixture of a monovalent cation and a divalent cation 
until equilibrium between the soil and solution is 
established, the proportions of exchangeable mono- 
valent and divalent cations present on the soil -exchange 
complex vary with the total-cation concentration as 
well as with the monovalent : divalent cation ratio of 
the salt solutions. Gapon(1933), Mattson and Wik- 
lander (1940), Davis (1945), and Schofield (1947) 
have proposed, in effect, that the influence of total- 
cation concentration is taken into account and a linear 
relation with the exchangeable monovalent: divalent 
cation ratio is obtained when the molar concentration 
of the soluble monovalent cation is divided by the 
square root of the molar concentration of the soluble 
divalent cation. 

Two ratios of the latter type, designated as the 
sodium-adsorption-ratio (SAR) and potassium-adsorp- 
tion-ratio (PAR) , are employed for discussing the 
equilibrium relation between soluble and exchangeable 
cations. The sodium-adsorption-ratio and potassium- 
ad sorption- ratio are defined asNa + /VlCa-H-+Mg ++ )/2 
and K + /V(Ca ++ + Mg ++ )/2, respectively, where Na%K + , 
Ca ++ , and Mg ++ refer to the concentrations of the desig- 
nated soluble cations expressed in milliequivalents per 
liter. 

The relationship between the sodium-adsorption- 
ratio and the ratio exchangeable sodium : (exchange 
capacity minus exchangeable sodium) at the saturation 
moisture percentage for 59 soil samples representing 12 
sections in 9 Western States is shown in figure 9. A 
similar relationship involving the potassium-adsorption 
ratio, exchange capacity, and exchangeable potassium 
is given in figure 10. The correlation coefficients for 
the two sets of values are sufficiently good to permit 
practical use of the relations. Data for soils having 
exchangeable sodium/ (exchange capacity minus ex- 
changeable sodium) and exchangeable potassium/ 
(exchange capacity minus exchangeable potassium) 
ratios greater than 1, which correspond to exchange- 
able-cation-percentages of more than 50, are not in- 
cluded in the graphs. Limited data indicate that for 
these soils the relations shown in the graphs are some- 
what less precise. Using the data presented in figure 9, 
the relation between the exchangeable-sodium-percent- 
age (ESP), and the sodium-adsorption-ratio (SAR) is 
given by the equation : 



ESP 



100 ( -0.0126+ 0.01475 SAR) 
1 + ( - 0.0126 + 0.01475 SAR ) 



Similarly, the relation between the exchangeable- 
potassium-percentage (EPP) and the potassium- 
adsorption-ratio (PAR) is given by the equation : 



EPP= 



100 (0. 0360 + 0.1051 PAR) 
T + ( 0.0360 + O1051 PAR) 



The former equation was employed to obtain the aver- 
age relation between exchangeable-sodium-percentage 
and the sodium-adsorption-ratio, which is shown by the 
nomogram given in figure 27, chapter 6. 

Chemical Analyses of Representative Soil 

Samples 

Data of typical chemical analyses of saline, non- 
saline-alkali, and saline-alkali soil samples are given 
in table 5. Similar analyses of samples of normal soils 
from arid regions are also given for comparative pur- 
poses. These analyses are presented to show the 
differences in the chemical characteristics of the four 
classes of soils and to illustrate how the analyses may be 
interpreted and cross-checked for reliability. 

Nonsa line-Nona I kali Soils 

Samples numbered 2741, 2744, and R-2867 are 
classed as normal with respect to salinity and alkali, 
because the electrical conductivity of their saturation 
extracts is less than 4mmhos/cm. and their exchange- 
able-sodium-percentage is less than 15. The reaction 
of the samples ranges from slightly acid to slightly 
alkaline. While the composition of the soluble ions 
varies somewhat, the amounts present are small, and 
all of the saturation extracts have low sodium-adsorp- 
tion-ratios. Alkaline-earth carbonates may or may not 
be present. Also, gypsum may or may not be present, 
although none of the samples selected contains this 
constituent. 

Saline Soils 

The electrical conductivity of the saturation extracts 
of these samples is in excess of 4 mmhos/cm., but the 
exchangeable-sodium-percentage is less than 15. In 
no case does the pH reading exceed 8.5. Chloride and 
sulfate are the principal soluble anions present in these 
samples, the bicarbonate content is relatively low, and 
carbonate is absent. The soluble-sodium contents ex- 
ceed those of calcium plus magnesium somewhat, but 
the sodium-adsorption-ratios are not high. Gypsum 
and alkaline-earth carbonates are common constituents 
of saline soils. As shown by the values for the electri- 
cal conductivity of the saturation extracts, the salinity 
levels are sufficiently high to affect adversely the growth 
of most plants. Reclamation of the soils will require 
leaching only, providing drainage is adequate. 

Nonsa line-Alkali Soils 

The exchangeable-sodium-percentages of these soil 
samples exceed 15, but the soluble-salt contents are low. 



SALINE AND ALKALI SOILS 



27 




20 3 40 

SODIUM -ADSORPTION-RAT 10 

Figure 9.-Exchangeable-sodium ratio '^/'■^^^ J as related to the sodium-adsorption-ratio (SAR) of the saturation extract. 

ES, exchangeable sodium; CEC, cation-exchange-capacity. 



28 



AGRICULTURE HANDBOOK 60, U. S. DEPT. OF AGRICULTURE 



1.00 




2 3 4 5 

POTASS IUM-A0S0RPT ION -RATIO 



PAR 



Figure IO.-Exchangeable-potassium ratio (EP/WEC—EP]) as related to the potassium-adsorption-ratio (PAR) of the saturation 

extract. EP, exchangeable potassium; CEC, cation-exchange-capacity. 



SALINE AND ALKALI SOILS 



29 



Table 5. — Chemical analyses of soil samples from arid regions 

Soil Determinations 



Soil and sample N o. 


Satura- 
tion 

percent- 
age 


pHof 
satu- 
rated 
soil 


Cation- 
exchange - 
capacity 


Exchangeab 

Na K 


le-cation-percentagej 


1 


&ypsun 


Alkaline- 
earth car- 
bonates * 


Ca 


Mg 


H 




















Meq./ 




Normal soils: 






Meq./lOOgm. 












100 gm. 




2741. 


35.6 


6.4 


20.3 


2 


8 




29 


7 





— 


2744 


32.4 


7.8 


29.4 


10 


1 


• • •••*}^ 










+ 


R - 2 8 6 7 . 


40.4 


7.9 


17.4 


3 


1 


* 












Saline soils: 






















574 


52.0 


7.9 


14.4 


13 


3 


+ 







7.1 


+ 


756 


46.5 


8.0 


17.0 


8 


2 












+ 


575 


40.0 


8:0 


18.6 


10 


17 


* 










+ 


Nonsaline-alkali soils: 






















2747 


58.8 


8.3 


33.4 


18 


3 




******** 








+ 


2738, 


61.2 


7.3 


34.2 


24 


2 


31 


30 


13 







535 


38.7 


9.6 


21.9 


46 


32. 












+ 


Saline-alkali soils: 






















2739 


61.5 


7.3 


35.7 


26 


2 


27 


35 


10 





— 


2740 


59.7 


7.8 


40.3 


26 


2 


* * 


lil**4»4 




42 2 


+ 


536 


35.8 


9.3 


26.2 


63 


8 






8 


0' 


+ 



Saturation Extract Determinations 



Soil 
and 


Elec- 
trical 


Cations 


Anions 


Sodium- 
adsorp- 






















tion- 

ratio 

(SAR) 


sample 


conduc- 






















No. 


tivity 


Ca++ 


Mg++ 


Na+ 


K+ 


Total 


co 3 = 


HC0 3 " 


sor 


ci- 


Total 


Normal 


Mmhos/ 
























soils: 


cm. 


Meq./L 


Meq.jl. 


Meq./l. 


Meq./L 


Meq.jl 


Meq.jl. 


Meq./L 


Meq.jl 


Meq./L 


Meq.jl. 




2741 


0.60 


2.71 


2.26 


1.20 


0.91 


7.08 





2.60 


2.09 


0.87 


5. 56 


0.8 


2744.. 


1.68 


3.33 


1.94 


12.2 


.70 


18.17 





6. 14 


4.28 


4.93 


15.35 


7.5 


R-2867. 


.84 


2. 76 


1.69 


5.22 


.18 


9.85 





6.63 


2.67 


.44 


9.74 


3.5 


Saline soils: 


























574.. . 


13.9 


31.5 


37.2 


102.0 


.21 


170.91 





4.50 


90.0 


78.0 


172.50 


17.4 


756 


12.0 


37.0 


34.0 


79.0 


40 


150.40 





7.20 


62.2 


47. 


148.40 


13.3 


575 


8.8 


28.4 


22.8 


53.0 


1:10 


105.30 





5.20 


74.0 


29.0 


108.20 


10.5 


Nonsaline- 


























alkali 


























soils: 


























2747.. 


1.74 


1.10 


1.42 


15.6 


.42 


18. 54 




6.51 


8.48 


2.86 


17.85 


13.9 


2738. 


2.53 


1.41 


1.01 


21.5 


.28 


24.20 


8 


3.29 


3.80 


16.7 


23.79 


19.6 


VUV 4 * • • - 


3. 16 


1.10 


.30 


29.2 


4. 10 


34.70 


8.40 


18.70 


4. 60 


7.50 


39.20 


35.0 


Saline- 


























alkali 


























soils: 


























2739 


9. 19 


6.73 


9.85 


79.5 


.48 


96.56 





2.35 


20.1 


72.0 


94. 45 


27.6 


2740.. 


16.7 


32.4 


38.3 


145.0 


.51 


216.21 





3.29 


105.0 


105.0 


213.29 


24.4 


536 


5.6 


.60 


.90 


58.5 


1.6 


61.60 


5.00 


19.9 
2 Indue 


21.5 


16.3 


62.70 


67.6 


1 +, Presen 


it; -, absei 


it. 












ies 32.0 n 


ieq./l. Of ? 


nF0 3 . 





Usually the pH readings are greater than 8.5, but they 
may be lower if the exchangeable-sodium-percentage 
does not greatly exceed 15 (sample No. 2747) or if 
alkaline-earth carbonates are absent (sample No. 
2738). Gypsum seldom occurs in these soils. The 
chief soluble cation is sodium, and appreciable amounts 
of this cation may be present as the bicarbonate and 
carbonate salts. The sodium-adsorption-ratio of the 
saturation extract may be quite high. Sample No. 2738 



is an example of a nonsaline-alkali soil that is free 
of alkaline-earth carbonates and contains some ex- 
changeable hydrogen. Replacement of exchangeable 
sodium will be required for its reclamation. Gypsum 
is a suitable amendment, but the application of acid 
or acid-forming amendments may cause excessive soil 
acidity unless limestone is also applied. The applica- 
tion of limestone alone will tend to replace the ex- 
changeable sodium. Sample Nos. 2747 and 535 will 



30 



AGRICULTURE HANDBOOK 60, U.S. DEPT. OF AGRICULTURE 



also require replacement of exchangeable sodium for 
reclamation; but, owing to the presence of alkaline- 
earth carbonates, acid, any acid -forming amendment, 
or gypsum may be applied. The application of lime- 
stone alone will obviously be of no value. 

Saline-Alkali Soils 

Soils of this class are characterized by their appre- 
ciable contents of soluble salts and exchangeable 
sodium. The electrical conductivity of the saturation 
extract is greater than 4 mmhos/cm., and the exchange- 
able-sodium-percentage exceeds 15. The pH reading 
may vary considerably but is commonly less than 8.5. 
Except that a higher proportion of the soluble cations 
consists of sodium, the composition of the soluble salts 
usually is similar to that of saline soils. Although 
only the most salt-sensitive plants will be affected by 
the salinity level of sample No. 536, the exchangeable- 
sodium-percentage is too high to permit the growth of 
most crops. Both replacement of exchangeable sodium 
and leaching are required for reclamation of these soils. 
With respect to the suitability of various amendments 
for the replacement of exchangeable sodium, sample 
No. 2739, like No. 2738, will require the application of 
soluble calcium, whereas sample No. 536, like samples 
2747 and 535, can be treated with soluble calcium, 
acid, or acid-forming amendments. Owing to its high 
content of gypsum, sampleNo. 2740 will not require the 
application of amendments for the replacement of 
exchangeable sodium. 

Cross-Checking Chemical Analyses for 
Consistency and Reliability 

A means of locating gross errors in the chemical 
analyses of soils is provided by the considerable num- 
ber of interrelations that exist among the values ob- 
tained for various determinations. An understanding 
of the principles involved in these interrelations aids 
in the interpretation of the analyses. 

Electrical conductivity and total cation CON- 
CENTRATION. -The EC of soil solutions and saturation 
extracts when expressed in millimhos per centimeter at 
25" C. and multiplied by 10 is approximately equal to 
the total soluble-cation concentration in milliequiva- 
lents per liter. 

Cation and anion CONCENTRATION .-The total solu- 
ble-anion concentration or content and the total soluble- 
cation concentration or content, expressed on an 
equivalent basis, are nearly equal. 

pH and carbonate AND BICARBONATE concentra- 
tions. — If carbonate ions are present in a soil extract 
in titratable quantities, the pH reading of the extract 
must exceed 9. The bicarbonate concentration seldom 
exceeds 10 meq./l. in the absence of carbonate ions, 
and at pH readings of about 7 or less seldom exceeds 
3 or 4 meq./ I. 

pH and calcium and magnesium concentrations. — 
The concentration of calcium and magnesium in a sat- 
uration extract seldom exceeds 2 meq./ I. at pH readings 
above 9. Therefore, calcium plus magnesium is low 



if carbonate ions are present in titratable amounts, and 
calcium plus magnesium is never high in the presence 
of a high concentration of bicarbonate ions. 

Calcium AND SULFATE IN A SOIL- WATER EXTRACT AND 

gypsum content of the soil. — The solubility of gyp- 
sum at ordinary temperatures is approximately 30 
meq./ I. in distilled water and 50 meq./ I. or more in 
highly saline solutions. However, owing to the com- 
mon ion effect, an excess of either calcium or sulfate 
may depress the solubility of gypsum to a value as low 
as 20 meq./ I. Hence, the saturation extract of a non- 
gypsiferous soil may contain more than 30 meq./ I. of 
both calcium and sulfate (i. e. saline soil No. 756), and 
that of a gypsiferous soil may have a calcium concen- 
tration as low as 20 meq./l. As a general rule, soils 
with saturation extracts that have a calcium concentra- 
tion of more than 20 meq./ I. should be checked for 
the presence of gypsum. 

pH and alkaline-earth CA RBO N ATES.-The pH 
reading of a calcareous soil at the saturation percentage 
is invariably in excess of 7.0 and generally in excess of 
7.5; a noncalcareous soil may have a pH reading as 
high as 7.3 or 7.4. 

pHand gypsum. — ThepH reading of gypsiferous 
soils at the saturation percentage is seldom in excess of 
8.2 regardless of the ESP. 

pH and ESP. -A pH reading at the saturation per- 
centage in excess of 8.5 almost invariably indicates an 
ESP of 15 or more. 

ESP and SAR.-ln general, ESP increases with SAR. 
There are occasional deviations, but generally low SAR 
values of the saturation extract are associated with low 
ESP values in the soil, and high SAR values denote high 
ESP values. 

CEC and SP.-Because both cation-exchange-capa- 
city and moisture-retention properties are related to 
the texture of soils, there generally exists a fair corre- 
lation among these properties, particularly in soils with 
similar parent materials and mode of origin. 

Factors That Modify the Effect of Exchangeable 

Sodium on Soils 

As might be expected, alkali soils having similar ex- 
changeable-sodium-percentages may vary considerably 
with respect to their physical properties, their ability to 
produce crops, and their response to management prac- 
tices, including the application of amendments. Al- 
though the reasons for the variable behavior of alkali 
soils are imperfectly understood, experience and limited 
data indicate that the effect of exchangeable sodium 
may be modified by several soil characteristics. Deter- 
minations of some or all of these characteristics are 
often of value in the investigation of alkali soils. 

Texture 

It is well known that the distribution of particle sizes 
influences the moisture retention and transmission 
properties of soils. Particle-size analysis may be made, 
using Method 41. As a rule, coarse-textured soils have 
low-moisture retention and high permeability, whereas 



SALINE AND ALKALI SOILS 



31 



fine-textured soils have high-moisture retention and 
generally have lower permeability. However, owing 
to a high degree of aggregation of the particles, there 
are notable examples of fine-textured soils that are 
moderately permeable. The presence of a high per- 
centage (50 or more) of silt-size particles (effective 
diameter 2/* to 50/x) often causes soils to have relatively 
low permeability. There is also evidence that some 
silt-size particles, presumably those having a platy 
shape, are more effective in reducing permeability than 
others. In general, the physical properties of fine- 
textured soils are affected more adversely at a given 
exchangeable-sodium-percentage than coarse-textured 
soils. For example, the hydraulic conductivity of a 
coarse-textured soil having an exchangeable-sodium- 
percentage of 50 may be as great as that of a fine- 
textured soil having an exchangeable-sodium-percent- 
age of only 15 or 20. Inasmuch as fine-textured soils 
generally have higher cation-exchange-capacities than 
coarse-textured soils, expressing the critical levels of 
sodium in milliequivalents per 100 gm. tends to elimi- 
nate the texture factor in evaluating the effect of 
exchangeable sodium. 

Surface Area and Type of Clay Mineral 

Soil particles may be considered to have two types 
of surfaces: external and internal. Primary minerals 
such as quartz and feldspars and the clay minerals kao- 
iinite and illite have external surfaces only. Clay min- 
erals of the expanding lattice type such as montmorillo- 
nite, which exhibits interlayer swelling, have'internal as 
well as external surfaces. The external surface area 
of soils is directly related to texture, whereas internal 
surface area is related to the content of minerals that 
exhibit interlayer swelling. Determinations of the 
amounts of ethylene glycol retained as a monomolec- 
ular layer by heated and unheated samples of soil 
(Method 25) permit estimation of the external and the 
internal surface areas, provided appreciable amounts 
of vermiculite and endellite minerals are not present. 
In any case, the ethylene glycol retained bv unheated 
soil in excess of that retained by a corresponding heated 
sample is an index of interlayer swelling. 

As determined by Method 25, the external surface 
areas of most soils lie in the range 10 to 50 m. 2 /gm. 
(square meters per gram), whereas the internal surface 
area varies to a greater extent, being nil in soils that 
contain no interlayer swelling minerals and as high 
as 150m. 2 /gm. or more in soils with a high content of 
expanding lattice-type minerals. X-ray diffraction 
patterns indicate that the clay fraction (particles <2/t 
effective diam.) of many soils of arid regions are pre- 
dominantly interstratified mixtures of various propor- 
tions of montmorilloniteand illite, although sometimes 
individual crystals of these minerals occur. The 
amount of kaolinite present is usually small. 

It is generally recognized that soils containing clay 
of the expanding lattice (montmorillonitic) type exhibit 
such properties as swelling, plasticity, and dispersion 
to a greater extent than soils containing equivalent 



amounts of nonexpanding lattice (illitic and kaolinitic) 
clays, especially when appreciable amounts of ex- 
changeable sodium are present. Whether the more ad- 
verse physical properties imparted by the former type 
of clays are caused by their greater total surface area 
or to the fact that they exhibit interlayer swelling is 
not definitely known. Further studies may show that 
the susceptibility of soil to injury by exchangeable 
sodium is related to total surface area as measured by 
ethylene glycol retention. 

Potassium Status and Soluble Silicate 

Several medium- to fine-textured alkali soils have 
been examined at the Laboratory and have been found to 
be much more permeable than would ordinarily be ex- 
pected on the basis of their high exchangeable-sodium- 
percentages. In some cases, the permeability is such 
that the soils can be leached readily with large quanti- 
ties of irrigation water and the excess exchangeable 
sodium removed without the use of chemical amend- 
ments. The soils have several characteristics in com- 
mon, which include a high pH value (9.0 or higher), 
a high exchangeable-potassium-percentage (25 to 40), 
and an appreciable content of soluble silicate. The 
silicate concentration of the saturation extracts of these 
soils has been found to vary from 5 to 40 meq./l., and 
additional quantities of this anion as well as sodium 
are removed upon leaching. As shown by ethylene 
glycol retention, Dyal and Hendricks (1952) and Bower 
and Gschwend (1952), saturation of montmorillonite 
clays and soils with potassium followed by drying de- 
creases interlayer swelling. Moreover, Mortland and 
Gieseking (1951) have shown by means of X-ray 
diffraction studies that montmorillonite clays, when 
dried in the presence of potassium silicate, are changed 
to micalike clays that would have less tendency to swell 
and disperse under the influence of exchangeable 
sodium. Ethylene glycol retention determinations 
made on some of the alkali soils having high exchange- 
able-potassium-percentages and containing appreciable 
soluble silicate give relatively low values for interlayer 
swelling. While further research is needed to clarify 
the role of exchangeable potassium and soluble silicate, 
there is a distinct indication that alkali soils containing 
unusually high amounts of these constituents are less 
susceptible to the development of adverse physical 
conditions. 

Organic Matter 

While the organic-matter content of soils of arid 
regions is usually low under virgin conditions, it com- 
monly increases with the application of irrigation water 
and cultivation, especially when crop management is 
good. Aside from its value as a source of plant 
nutrients, organic matter has a favorable effect upon 
soil physical properties. 

There is considerable evidence that organic matter 
tends to counteract the unfavorable effects of exchange- 
able sodium on soils. Campbell and Richards (1950) 



32 



AGRICULTURE HANDBOOK 60, V. S. DEPT. OF AGRICULTURE 



£ 



- SOIL SAMPLE 



HYDRAULIC 
CONDUCTIVITY 



r 



1 



SATURATED PASTE 



H 



NOT A 
PERMEABILITY 

PROBLEM 



• 



\ 



/ POSSIBLE \ 
/ TOXICITY \ 



NOT A 
SALINITY 

PROBLEM 



jL 



/ 



SAR 



I 



H L 



TOTAL 
EXTRACTABLE 
I SODIUM - 

It 



v FROM r ' 

^HIGH ESP/ / POSSIBLE \ 

V ^' \ TOXIC j 

\ IONS / 

\ / 



il 



H 



i 



'8 



i 



pH, 



SP 



SATURATION 
EXTRACT 



CONDUCTIVITY 

OF 

SATURATION 1 

EXTRACT 



l 



EXCH. 
POTAS- 
SIUM 



i 



EXCHANGEABLE 
SODIUM 



^ 



ESP 



CEC 



l_ 



H 



jL 



NOT AN 

ALKALI 

PROBLEM 



71 



/ 



s 



\ 



\ 



/ 



GYPSUM 



■*- 



H 



ALKALI 
PROBLEM 



/ POSSIBLE \ 

UNFAVORABLE] 

i PHYSICAL ' 

\ CONDITION / 

V / 



t 



ALKALINE 

EARTH 

CARBONATES 



ACID OR 
CALCIUM 
AMENDMENT 



CALCIUM 
AMENDMENT 



1 



LEACHING 
PROBLEM 



H 



Figure II. -Sequence of determinations for the diagnosis and treatment of saline and alkali soils: H, High; L, low; Rs> 
electrical resistance of soil paste; SAR, sodium-adsorption-ratio; ESP, exchangeable-sodium-percentage; CEC, cation- 
exchange-capacity. 



SALINE AND ALKALI SOILS 



33 



and Fireman and Blair 5 found that peat and muck soils 
containing appreciable quantities of exchangeable 
sodium had good physical properties, and numerous 
investigators have demonstrated a beneficial effect of 
organic matter additions upon alkali soils. For ex- 
ample, Bower and associates (1951) found that the 
application of manure at the rate of 50 tons per acre 
to an alkali soil of the "slick spot" type increased the 
degree of aggregation of the surface soil significantly 
and the infiltration rate approximately threefold. The 
available data indicate that organic matter improves 
and prevents deterioration of the physical condition 
of the soil by its interaction with the inorganic cation- 
exchange material, by serving as energy material for 
micro-organisms which promote the stable aggregation 
of soil particles, and by decreasing the bulk density of 
soils. 

The organic-matter content of soils is ordinarily ob- 
tained by multiplying the organic-carbon content by 
1.72. The dry-combustion method is most accurate 
for the determination of organic carbon, but it is time- 
consuming and cannot be applied to soils containing 
carbonates. Wet-combustion methods such as the one 
given in Method 24 are suitable for use on soil contain- 
ing carbonates, but the application of a correction factor 
is required to compensate for the incomplete oxidation 
of the organic matter. 

Sequence of Determinations for Soil Diagnosis 

The salinity status and the hydraulic conductivity 
are measured for all samples. The sequence of further 
determinations depends on whether the result obtained 
from a previous determination (fig. 11) is considered 
to be highorlow. Criteria for distinguishing high and 
low values are discussed in chapter 6. 

The determinations are ordinarily discontinued when 
the guide I i nes of the two mai n branches of the d iagram 
lead to a heavy-walled box, except in the case of an 



'Fireman, M ., and Blair, 
ANALYSES OF SOILS FROM THE 

[Unpublished.] J anuary 1949. 



G. Y. CHEMICAL AND PHYSICAL 

HUMBOLDT PROJECT, NEVADA. 



alkali problem where alkaline-earth carbonates should 
also be determined if the use of acid or acid-forming 
amendments is contemplated. At two places in the dia- 
gram, dotted lines indicate where optional alternate de- 
terminations can be made. The alternate determina- 
tions cost somewhat less but have lower reliability. 

Hydraulic-conductivity measurements on disturbed 
samples provide an indication of the moisture-transmis- 
sion rate of the soil. It has been found for most soils 
that exchangeable sodium is not excessive if this rate is 
high. However, coarse soils such as sands and peats 
may contain sufficient amounts of exchangeable sodium 
to be toxic to plants and yet have high permeability. 
If the hydraulic conductivity is low, the total extract- 
able sodium or the sodium-adsorption-ratio (SAR) 
should be determined. If either of these is low, the 
low hydraulic-conductivity value previously obtained 
may be the result of an inherently unfavorable physical 
condition related to texture, low content of organic 
matter, or high-swelling type clay rather than the pres- 
ence of exchangeable sodium. For these samples, or- 
ganic matter, ethylene glycol retention, and particle-size 
analyses may yield useful information. 

If the total extractable-sodium content or the SAR 
value is high, the exchangeable sodium should be de- 
termined or, alternatively, the exchangeable-sodium- 
percentage can be estimated from the SAR value. If 
the exchangeable-sodium content or exchangeable- 
sodium- percentage is high, a gypsum determination 
should be made. A high-gypsum value indicates that 
leaching only is required, while a low-gypsum value 
indicates need for amendments,. When there is a low- 
gypsum value, the presence or absence of alkaline-earth 
carbonates is ascertained to indicate the type of chemi- 
cal amendment that can be used for the replacement of 
exchangeable sodium. The addition of amendments 
should be followed by leaching. Other determinations, 
such as pH, saturation percentage, cation-exchange- 
capacity, exchangeable potassium, toxic ions, and tex- 
ture, provide additional information and are made if 
circumstances warrant. 



Chapter3 



Improvement and Management of Soils in Arid 
and Semiarid Regions in Relation 
to Salinity and Alkali 



The development and maintenance of successful irri- 
gation projects involve not only the supplying of irri- 
gation water to the land but also the control of salinity 
and alkali. The quality of irrigation water, irrigation 
practices, and drainage conditions are involved in sa- 
linity and alkali control. In establishing an irrigation 
project, soils that are initially saline require the removal 
of the excess salts and may require chemical amend- 
ments in addition to an adequate supplv of irrigation 
water. On the other hand, soils that initially are non- 
saline may become unproductive if excess soluble salts 
or exchangeable sodium are allowed to accumulate 
because of improper irrigation and soil management 
practices or inadequate drainage. 

Basic Principles 

Although farming practices may vary from one irri- 
gated area to another, the following general principles 
related to salinity and alkali have universal application. 

Plant growth is a function of the total soil-moisture 
stress, which is the sum of the soil-moisture tension and 
the osmotic pressure of the soil solution. Through 
controlled leaching, the osmotic pressure of the soil 
solution should be maintained at the lowest feasible 
level ; and, by a practical system of irrigation, the soil- 
moisture tension in the root zone should be maintained 
in a range that will give the greatest net return for the 
crop being grown. 

Water flows in both saturated and unsaturated soil 
in accordance with Darcy's law, which states that the 
flow velocity is proportional to the hydraulic gradient 
and the direction of flow is in the direction of the 
greatest rate of decrease of hydraulic head. This prin- 
ciple makes it possible to determine the direction of 
flow of ground water by simple methods. A knowl- 
edge of the source and direction of flow of ground 
water is especially useful in solving drainage problems. 

Soluble salts in soil are transported bv water. This 
is an obvious but basic principle pertaining to the con- 
trol of salinity. Salinity, therefore, can be controlled 
if the quality of the irrigation water is satisfactory and 
if the flow of water through the soil can be controlled. 

34 



The concentration of soluble salts in the soil solution 
is increased as water is removed from the soil by evapo- 
ration and transpiration. Desiccation of surface soil 
by transpiration and by evaporation creates a suction 
gradient that will produce an appreciable upward move- 
ment of water and salt. This upward flow, especially 
if the water table is near the soil surface, is a process 
by which many soils become salinized. 

Sol uble salts i ncrease or decrease i n the root zone, de- 
pending on whether the net downward movement of 
salt is less or greater than the net salt input from irriga- 
tion water and other sources. The salt balance in soil, 
as affected by the quantity and quality of irrigation 
water and the effectiveness of leaching and drainage, is 
of paramount importance. If irrigation agriculture is 
to remain successful, soil salinity must be controlled 
(Scofield, 1940). 

Equilibrium reactions occur between the cations in 
the soil solution and those adsorbed on the exchange 
complex of the soil . The use of amendments for chang- 
ing the exchangeable-cation status of soil depends upon 
these equilibrium reactions. Adsorption of excessive 
amounts of sodium is detrimental to the physical status 
of the soil and may be toxic to plants. When the ex- 
changeable-sodium content of soil is excessive or tends 
to become so, special amendment, leaching, and man- 
agement practices are required to improve and main- 
tain favorable soil conditions for plant growth. 

Whether soil particles are flocculated or dispersed 
depends to some extent upon the exchangeable-cation 
status of the soil and, also, upon the ionic concentration 
of the soil solution. Soils that are flocculated and 
permeable when saline may become defloccu I ated when 
leached. 

Irrigation and Leaching in Relation to 

Salinity Control 

Irrigation is the application of water to soil for the 
purpose of providing a favorable environment for 
plants. Leaching, in agriculture, is the process of dis- 
solving and transporting soluble salts by the downward 
movement of water through the soil. Because salts 



SALINE AND ALKALI SOILS 



35 



move with water, salinity depends directly on water 
management i. e., irrigation, leaching, and drainage. 
These three aspects of water management should be 
considered collectively in the over-all plan for an irri- 
gated area if maximum efficiency is to be obtained. 

Irrigation 

Insubhumid regions, when irrigation is provided on 
a standby or supplemental basis, salinity is usually of 
little concern, because rainfall is sufficient to leach out 
any accumulated salts. But in semiarid or arid regions 
salinity is usually an ever-present hazard and must be 
taken into account at all stages of planning and 
operation. 

The subject of water quality in relation to irriga- 
tion is discussed at length in chapter 5 and is mentioned 
here only to emphasize the fact that water quality must 
be considered in determining the suitability of soils for 
irrigation. In general, waters with high salt contents 
should not be used for irrigation on soils having low 
infiltration and drainage rates. The higher the salt 
content of the water, the greater the amount of water 
that must be passed through the soil to keep the soluble- 
salt content at or below a critical level. Experience 
indicates that there are soils in which low water-move- 
ment rates make the cost of drainage so high that 
irrigation agriculture is not feasible under present 
economic conditions. 

Pumping from ground water for irrigation has sev- 
eral advantages. It often affords direct local control 
of the water table when water is pumped from uncon- 
fined or partially confined aquifers. This has been 
demonstrated in the Salt River Valley, Arizona, the San 
Joaquin Valley, California, and elsewhere. Wells can 
often be located on the farm, thereby eliminating the 
need for elaborate distribution systems. Water is avail- 
able for use at all times, which provides maximum flex- 
ibility in irrigation. If it is pbssibleto obtain irriga- 
tion water from both ground-water and surface sup- 
plies, a balance between the two sources can often be 
established to insure favorable drainage of the irrigated 
soils. Another indirect advantage of pumping water 
for irrigation comes from the fact that the direct visible 
cost of operating pumps causes the farmer to avoid the 
wasteful overuse of water which often is the cause of 
the need for drainage improvement. 

Excessive losses from water conveyance and distribu- 
tion systems must be prevented, otherwise drainage 
problems will be aggravated with attendant salinity 
hazards. Distribution systems and irrigation schedules 
should be designed so that water is available at times 
and in amounts needed to replenish the soil moisture 
without unnecessary use on irrigated fields and without 
regulatory waste of water which may directly or indi- 
rectly contribute to unfavorable drainage conditions. 
I n some cases, water is used under conti nuous free-flow 
systems to maintain water rights rather than on a basis 
of consumptive use. Salinity and drainage problems 
could undoubtedly be alleviated in some areas by 



changing to a system of direct charge for the volume 
of water used. 

The quantity of water available for irrigation may 
have a marked effect upon the control of salinity. In 
areas where water is cheap and large volumes are used, 
irrigation practices are often inefficient. Overuse and 
waste of irrigation water contribute to drainage diffi- 
culties and salinity problems. Efficient irrigation prac- 
tices can be developed more readily in the planning of 
irrigation systems than by applying corrective measures 
on the farm. Limited quantities of water should be 
supplied, based upon consumptive use and leaching re- 
quirements, for the area in question. Where an abun- 
dant supply of water is available for irrigation, restric- 
tions may become necessary if drainage problems arise. 
Water requirements for leaching are discussed in a 
following section. 

Lining canals to reduce seepage losses and the dis- 
tribution of water by underground pipe systems should 
receive careful consideration. M uch can be done in the 
layout of distribution systems to reduce seepage losses 
by locating canals and laterals properly. In some 
areas, earth and asphalt linings for irrigation canals 
have been used successfully. The buried asphalt mem- 
brane lining used by the United States Bureau of Recla- 
mation on a number of projects has been shown to be 
effective in reducing seepage losses. In the Coachella 
Valley, California, an underground concrete-pipe distri- 
bution system, and a concrete-lined main canal, serve 
approximately 70,000 acres of land. Reduction of 
seepage losses and improvement in drainage conditions 
were major factors in the selection of these facilities. 

Automatic control of distribution systems, combined 
with lined canals and laterals, is being used success- 
fully in Algeria and elsewhere to eliminate regulatory 
waste and to reduce the cost of operation. Automatic 
control makes water available at the farm at all times 
and allows water to be taken out or shut off from the 
main distribution system at laterals or at farm outlets 
at any time. All regulatory changes to maintain 
proper flow from the point of diversion to the farm are 
performed automatical ly . This el i mi nates waste on the 
farm and throughout the system. Older irrigation dis- 
tricts with drainage and salinity problems might well 
consider some of the advantages of the newly developed 
automatic distribution systems. A modernization of 
the distribution system in some cases may be the most 
economical way to solve a drainage problem. 

The selection of an irrigation method for applying 
water to the soil is related to salinity. The method 
that is best adapted in any particular case depends upon 
a number of conditions: The crop to be grown, topog- 
raphy, s °il characteristics, availability of water, 
soluble-salt content of the water, and salinity status of 
the soil. The primary objective of any irrigation 
method is to supply water to the soil so that moisture 
will be readily available at all times for crop growth, 
but soil salinity is definitely an influencing factor. 

It is desirable, both for plant use and for leaching, 
to apply the water uniformly over the irrigated area. 



36 



AGRICULTURE HANDBOOK 60, U. S. DEPT. OF AGRICULTURE 



The four principal methods used for the application of 
water are flooding, furrow, sprinkling, and sub- 
irrigation. 

The flooding method should be favored if salinity 
is a serious problem. Wild flooding, border-strip or 
border-check flooding, and basin flooding are used. 
Wild flooding is not practiced extensively, except for 
pastures, alfalfa, and small grains. This method can 
be used only in relatively level areas where water can be 
flooded over the surface without the use of levees or 
borders for control. The border-strip or border-check 
method of irrigation utilizes levees or borders for con- 
trol of the water. The water is not impounded by this 
method, except perhaps at the lower end of the strip, 
but is flooded over the surface and down the slope in 
the direction of the borders. It is adapted for use with 
alfalfa and grains and in orchards; but excessive water 
penetration near the head ditch and at the ends of the 
strips usually results. There is a tendency for insuf- 
ficient penetration to occur midway or two-thirds of the 
way down the strip which generally causes salt to 
accumulate in this location. 

The basin method of flooding is often used for 
orchards and various other crops in areas where water 
can be impounded in a rectangular basin. A variation 
of this method is the contour-basin method. Borders 
are constructed along the contours at intervals of about 
0.1 to . 2 foot. This allows larger basins to be made 
where there is appreciable slope. The basin methods 
of irrigation provide better control of the depths of 
water applied and greater uniformity in application 
than border or furrow methods. 

Furrow irrigation is well adapted to row crops and 
is suitable for use where the topography is too rough or 
steep for other methods. With this method there is a 
tendency for salts to accumulate in the ridges, because 
the leaching occurs only in the furrows. Wide-bot- 
tomed furrows that resemble narrow border strips have 
certain advantages for wetting the soil surface uni- 
formly and thereby controlling salt accumulation in a 
larger fraction of the root zone. Where the area is 
plowed and the surface soil is mixed occasionally, the 
i ncrease i n salt over a period of ti me may not be serious. 
If excess salt does accumulate, rotation of crops accom- 
panied by a change in method of irrigation to flooding 
or ponding is often possible as a salinity-control 
measure. In the furrow and border-check methods 
the length of run, size of stream, slope of the land, and 
time of application are factors that govern the depth 
and uniformity of application. Proper balance among 
these factors, therefore, is directly related to leaching 
and salinity control. 

Irrigation by sprinkling is generally more costly 
than by other methods and has not been used exten- 
sively until recent years. Originally this method was 
used primarily for orchards, truck crops, and nurseries ; 
but its use has been extended to include sugar beets, 
peas, beans, and many other crops. This method allows 
a close control of the depth of water applied and when 
properly used results in uniform distribution. It is 
often used i n areas where the slope is too great for other 



methods. There is a tendency to apply too little water 
by this method ; and, unless a special effort is made, 
leaching to maintain the proper salt balance will not be 
accomplished. 

Subirrigation is the least common of the various 
methods of irrigation and is not suitable for use where 
salinity is a problem. Even under the most favorable 
circumstances, this method does not appear to be suit- 
able for long-time use unless periodic leaching is accom- 
plished by rainfall or surface irrigations. 

Leaching 

The leaching of soluble salts from the root zone is 
essential in irrigated soils. The need for leaching can 
be illustrated by considering the effect that salts in 
irrigation water have upon the salinity of soil if no 
leaching occurs. Without leaching, salts accumulate 
in direct proportion to the salt content of the irrigation 
water and the depth of water applied. The concentra- 
tion of the salts in the soil solution results principally 
from the extraction of moisture from the soil by the 
processes of evaporation and transpiration. Assuming 
no precipitation of soluble constituents during the 
salinization process, the depth of irrigation water 
(D iw ) of known electrical conductivity (EC,,) that 
will contain sufficient salt to increase the electrical con- 
ductivity of the saturation extract of a depth of soil 
(D,) by an amount ( AEC e ) can be calculated from 
the equation : 

DiJD^idJd*) (SP/100) (A£C e /£Ciw) (1) 
where d s /d w is the ratio of the densities of the soil and 
the water, and SP is the saturation percentage. 6 

As an example, let: £C iw x 10 6 = 1,000, d s = 1.2 gm. 
cm." 3 ,J w = 1 gm. cm. -3 , and SP= 40. Make the calcu- 
lation for a change in electrical conductivity of the sat- 
uration extract of 4 mmhos/cm., or AEC e x 10 G = 
4,000. Substituting these values in the equation we 
find Z> iw /D s ^ 1.9. Thus less than 2 feet of reasonably 



6 For the purposes of this problem, electrical conductivity of 
water is a satisfactory measure of salt concentration. If Diw 
represents the depth of irrigation water applied and Z)sw 
represents the equivalent free depth of this water after entering 
the soil and being concentrated by transpiration and evapora- 
tion, then Diw/D*w=ECsw/ECivr, where the right-hand side 
of the equation is the ratio of the electrical conductivities of 
the soil water and the irrigation water. The conductivity of 
the saturation extract ECe provides a convenient scale for ap- 
praising soil salinity; therefore, consider the condition where the 
content of moisture in the soil is the saturation percentage and 
/\ECe is the increase in soil salinity produced by the water 
application under consideration. For this case, the depth of 
soil water (Daw) contained in a depth of soil (Ds) is given by 
the relation 

BW d w 100 Ua 
Substituting these values in the above equation and rearranging 

gives : 

D^^d* SP_ AEC e m 

D B d w ' 100 ' i?C iw V ; 

The equation makes it possible to calculate the depth of irri- 
gation water per unit depth of soil required to produce any 
Specified increase in soil salinity expressed in terms of &ECe t 
for any given conductivity of the irrigation water (ECiw) . 



SALINE AND ALKALI SOILS 



37 



good quality irrigation water contains sufficient salt to 
changea 1-foot depth of a salt-free loam soil to asaline 
condition, if there is no leaching or precipitation of salt 
in the soil. 

Hundreds of thousands of acres of land in western 
United States have been profitably irrigated for many 
years with water having an electrical conductivity value 
approximating 1,000 micromhos/cm. It is apparent 
that considerable leaching has been provided, since al- 
most enough salt is added to the soil each season to 
make the soil saline. With this quality of water, 
salinity troubles have occurred if the watkr table has 
approached to within 3 or 4 feet of the surface of the 
soil. In such cases extensive drainage and leaching 
operations have been necessary Some areas have been 
abandoned, because it was not economically feasible to 
provide soil drainage sufficient to take care-of required 
leaching. 

Leaching Requirement 

The leaching requirement may be defined as the 
fraction of the irrigation water that must be leached 
through the root z&e to control soil salinity at any 
specified level. 7 This concept has greatest usefulness 
when applied to steady-state water-flow rates or to total 
depths of water used for irrigation and leaching over 
a long period of time. Obtaining calculated or experi- 
mentally determined values of the leaching requirement 
is complicated by many factors, but it is profitable to 
consider some simplified theoretical cases. The leach- 
ing requirement will depend upon the salt concentra- 
tion of the irrigation water and upon the maximum 
concentration permissible in the soil solution. The 
maximum concentration, except for salt crusts formed 
by surface evaporation, will occur at the bottom of the 
root zone and will be the same as the concentration of 
the drainage water from a soil where irrigation water 
is applied with areal uniformity and with no excess 
leaching. Increase of the concentration of salts from 
the value existing in the irrigation water to the value 
occurring in the drainage water is related directly to 
consumptive use. On cropped areas this will consist 
mostly of water extracted from the soil by roots and 
so will depend on the salt tolerance of the crop. Ex- 



'In the report of the U. S. National Resources Committee 
(1938), C. S. Scofield with the cooperation of R. A. Hill, pro- 
posed a formula for what was called "service equivalence," 
in which the concentration of the drainage water and the con- 
centration of the irrigation water are taken into account. In 
addition to the salt removed through drainage, it is inherent 
with this formula that soluble salt is removed from the soil 
at a rate equal to the consumptive use of water times half the 
concentration of the irrigation water. 

A further contribution to this subject was made at the 
Irrigation Conference sponsored bv the Texas Agricultural Ex- 
periment Station at Ysleta, Texas: in July 1951." At this con- 
ference, F. M. Eaton proposed what he called a "drainage 
formula" for calculating the fraction of the irrigation water to 
be used for leaching. A private communication-to the Labora- 
tory from F. M. Eaton, under date of August 1952. 7 contained a 
mimeographed paper entitled "Formulas for estimating drain- 
age and gypsum requirements for irrigation waters," in which 
the bases for the Ysleta formula are presented. 



pressed in terms of electrical conductivity, the maxi- 
mum concentration of the soil solution should prob- 
ably be kept below 4 mmhos/cm. for sensitive crops. 
Tolerant crops like beets, alfalfa, and cotton may give 
good yields at values up to 8 mmhos/ cm., while a very 
tolerant crop like barley may give good yields at values 
of 12 mmhos/ cm. or higher. 

To illustrate the significance of the leaching require- 
ment, consider first the simplest possible case with the 
following assumed conditions : Uniform areal applica- 
tion of irrigation water; no rainfall; no removal of 
salt in the harvested crop; and no precipitation of sol- 
uble constituents in the soil. Also, the calculation will 
be based on steady-state water-flow rates or the total 
equivalent depths of irrigation and drainage waters 
used over a period of time. With these assumptions, 
moisture and salt storage in the soil, depth of root zone, 
cation-exchange reactions, and drainage conditions of 
the soil do not need to be considered, providing that 
drainage will permit the specified leaching. The leach- 
ing requirement (LR) as defined above, is simply the 
ratio of the equivalent depth of the drainage water to 
the depth of irrigation water (D dw /D iw ) and may be 
expressed as a fraction or as percent. Under the fore- 
going assumed conditions, this ratio is equal to the 
inverse ratio of the corresponding electrical conductiv- 
ities, that is: 



LR 



For field crops where a value of EC dVf = S mmhos/ cm. 
can be tolerated, the formula would be Z> dw /D lw = 
£C iw /8. For irrigation waters with conductivities of 
1, 2, and 3 mmhos/cm., respectively, the leaching re- 
quirements will be 13, 25, and 38 percent. These are 
maximum values, since rainfall, removal of salt by the 
crop, and precipitation of salts such as calcium carbo- 
nate or gypsum in the soil are seldom zero; and, if 
properly taken into account, these factors all would 
enter in such a way as to reduce the predicted value of 
the leaching requirement. 

Some care must be exercised in using equation 2, to 
make sure that the condition of steady-state or longtime 
average is understood. The equation does not apply 
if leaching is automatically taken care of by rainfall. 
Depending on soil texture and depth to water table, 
this may be the case even in semiarid regions, if the 
precipitation is confined to a small fraction of the year. 
Under these conditions, equation 1, which gives the 
buildup of salinity with depth of irrigation water 
applied, is useful for predicting salinity increases 
during an irrigation season or over a period of several 
seasons when rainfall may be abnormally low. 

As an average over a long time, the conductivity 
of the irrigation water used in equation 2 should be a 
weighted average for the conductivities of the rainwater 
(EC,,), and the irrigation water (£C iw ),i.e.: 



EC 



rw J 



(rw+lw) 



D TW +D 



Iw 



38 



AGRICULTURE HANDBOOK 60, U. S. DEPT. OF AGRICULTURE 



where D t w and D iw are the depths, respectively, of the 
rai nwater and i rrigation water enteri ng the soi I . Long- 
time averages may deviate markedly from actual con- 
ditions at any one time, as, for example, if the entire 
root zone is leached through during a short period of 
extra high rainfall. 

Information on the consumptive use of water by the 
crop is necessary if the leaching-requirement concept 
is to be used for determining either the depth of irri- 
gation water that must be applied or the minimum 
depth of water to be drained, in order to keep the soil 
salinity from exceeding a specified value. The depth 
of irrigation water (D iw ) is related to consumptive use, 
(/) cw ) and the equivalent depth of drainage water 
( D dw ) by the equation : 

D lw =D cw +D^ (4) 

Using equation 2 to eliminate Z) dw from equation 4 
gives: 

D lw =D cw l(l-LR) (5) 

Expressing the leaching requirement (LR) in this equa- 
tion in terms of the conductivity ratio in equation 2 
gives: 

Dl w = KEc^-mJ ™ ( 6) 

The depth of irrigation water (Z) iw ) is thus expressed 
in terms of the electrical conductivity of the irrigation 
water and other conditions determined by crop and 
climate; namely, consumptive use and salt tolerance of 
the crop. The salt tolerance of the crop is taken into 
account in the selection of permissible values of £C dw . 
Equations 5 and 6 are subject to the assumptions made 
in deriving equation 2. 

Under actual farming conditions, the depth of water 
applied per irrigation and the areal uniformity of 
application are certainly not precisely controlled. 
M easured water application efficiencies often run as low 
as 25 percent and seldom exceed 80 percent. Under 
these conditions, high precision in the determination 
of the leaching requirement has little significance. A 
formula like equation 2 would appear to have greatest 
usefulness in connection with the more saline irrigation 
waters, and for this case it appears to be justifiable to 
disregard the salt removed from the soil in the harvested 
crops. Consider alfalfa growing in the Imperial Val- 
ley, California, where 6 tons per acre of sun-cured hay 
is a common annual yield. The salt added to the soi I in 
the irrigation water consumed by this crop would be 
about 4 tons. Of this salt, not more than 0.4 ton would 
be removed in the harvested crop. Under these condi- 
tions, therefore, neglecting the salt removed in the crop 
overrates the salt input to the soil by a factor of about 
one-tenth. Taking £C dw = 8 and EC iw = 1, the calcu- 
lated steady-state leaching requirement for salt-tolerant 
crops of the I mperial Valley is 13 percent. A fractional 
error of one-tenth in this value would not be serious, 
in view of other uncertainties involved in the practical 
use of the figure. 

The relative significance of the salt removed in the 
harvested crop will increase as the salt input from irri- 



gation water decreases, but for soils with normal 
drainage the practical usefulness of a calculated value 
of the leaching requirement decreases as the salinity 
of the irrigation water decreases. A special case exists 
where leaching is severely restricted by low soil 
permeability and the salt content of the water is also 
very low. Under these conditions, salt removed from 
the soi I in the harvested crop might conceivably become 
an important factor determining the permanence of 
irrigation agriculture. 

The steady-state leaching requirement (equation 2), 
expressed in terms of electrical conductivity, is con- 
venient where soil moisture availability to plants and 
osmotic pressure relations are the principal concern. 
Cation exchange is known to effect a change in the 
relative composition of irrigation and drainage waters, 
but this process is stoichiometric and does not enter 
explicitly in the equation. It may happen, however, 
that with a particular irrigation water and a particular 
crop, some specific toxic constituent as, for example, 
the chloride ion or boron, might comprise the most 
critical problem. A leaching requirement for this con- 
stituent could then be calculated, provided some 
maximum permissible concentration of the toxic ion 
C dw in the water draining from the soil can be specified 
and provided also that the other assumptions pre- 
viously made are tenable. The leaching requirement 
equation then becomes : 



Mw C. 



dw 



where C iw is the concentration of the toxic ion in the 
irrigation water. 

There will be instances, of course, where precipita- 
tion of soluble constituents in the soil cannot be neg 
lected when calculating the leaching requirement. Gyp- 
sum is deposited in soils from some irrigation waters. 
Data are being accumulated on the precipitation of cal- 
cium and magnesium with bicarbonate in the irrigation 
water. This latter reaction is considered in chapter 5 
on irrigation water quality. Taking precipitation 
effects into account complicates a leaching requirement 
equation and will not be included in the present dis- 
cussion. It should be recalled again that the foregoing 
equations are based on the assumptions: uniform water 
application to the soil, no precipitation of soluble salt 
in the soil, negligible salt removal in the harvested 
crop, and soil permeability and drainage adequate to 
permit the required leaching. 

Quantitative consideration of the leaching require- 
ment is important when drainage is restricted or when 
the available irrigation water is efficiently used. If a 
large fraction of the water diverted for irrigation is 
wasted in various conveyance, regulatory, and, espe- 
cially, application losses, then estimates of leaching re- 
quirement have little practical significance. 

Leaching Methods 

Leaching can be accomplished by ponding an appre- 
ciable depth of water on the soil surface by means of 
dikes or ridges and thus establishing downward water 



SALINE AND ALKALI SOILS 



39 



movement through the soil. This is the most effective 
procedure that can be used for removing excess soluble 
salts from soil. Contour checks can be used for pond- 
ing water on the soil where there is considerable slope. 
Contour borders ranging from 1.5 to 4ft. or more high 
are constructed at elevation intervals ranging from 0.2 
to 0.5 ft. Overflow gates, placed in the borders con- 
necting adjacent plots, facilitate the control of water 
and allow a number of contour checks to be kept full 
simultaneously. Frequent applications of excess irri- 
gation water applied by flooding between border strips 
while a crop is being grown are sometimes used for 
leaching. The effectiveness depends upon how uni- 
formly the water is applied and how much water passes 
through the soil. Either continuous flooding or peri- 
odic water applications may be used for leaching. If 
the soil transmits water slowly, periodic drying may 
improve infiltration rates. 

In cold climates, leaching operations can often be 
conducted in the fall after the crops mature and before 
the soil freezes. In warmer climates, leaching opera- 
tions can be conducted during winter when the land 
would otherwise be idle. At this time, also, water may 
be more plentiful and the water table and drainage con- 
ditions more favorable than during the regular irriga- 
tion season. Unless drainage is adequate, attempts at 
leaching may not be successful, because leaching re- 
quires the free passage of water through and away from 
the root zone. Where drainage is inadequate, water 
applied for leaching may cause the water table to rise 
so that soluble salts can quickly return to the root zone. 

Visible crusts of salt on the surface of saline soils 
have sometimes led to the use of surface flushing for 
salt removal, i. e., the passing of water over the soil 
surface and the wasting of the runoff water at the 
bottom of the field. This method does not appear to 
be sufficiently effective to be worth while for most field 
situations. All known tests of the flushing method 
under controlled conditions confirm this conclusion. 
Turbulence in the flowing water causes some mixing, 
but mostly the water at the soil surface that contacts 
and dissolves the salt moves directly into the dry soil 
during the initial wetting process when the infiltration 
rate is highest. In one test the salt added to the soil 
in the water used for flushing exceeded the amount of 
salt removed in the waste water. 

The depth of water required for irrigation and leach- 
ing and the effect of leaching on the depth to water 
table can be estimated with the aid of the nomograms 
given in figure 8, chapter 2. The following examples 
will serve to illustrate the use of the nomograms in 
connection with irrigation, leaching, and drainage. 

(a) For a uniform soil with an initial moisture per- 
centage of 10, an upper limit of field moisture of 20 
percent, and a bulk density of 1.6 gm. cm.?, how 
deeply will a 6-in. irrigation wet the soil? In the left 
nomogram of figure 8, place a straightedge on 1.6 of 
the scale I^ and on 10 of scale A. Scale Ci then indi- 
cates that 1.94 in. of water are required to raise the 
moisture content of 1 foot of this soil by 10 percent. 



Therefore, 6/1.94=3.09 ft.=37 in. is the depth of 
wetting. 

(b) For a uniform soil with an initial moisture con- 
tent of 12.5 percent, an upper limit of field moisture of 
25 percent, and a bulk density of 1.3 gm. cm.?, what 
depth of water must be applied to make 3 in. of water 
pass through the soil at the4-ft. depth? Evidently the 
moisture content of the surface 4 ft. of soil must be 
increased by 12.5 percent before leaching will occur. 
Place a straightedge on 1.3 of the left nomogram of 
scale B, (fig. 8), and on 12.5 of scale A. Scale d 
then indicates that 2 in. of water per foot of soil are 
required to change the moisture percentage of this soil 
from 12.5 to 25. Eight inches of water would be re- 
quired to bring the top 4 ft. of soil to the upper limit 
of moisture retention, and therefore 11 in. of irrigation 
water should be applied in order to cause 3 in. of water 
to pass below the 4-ft. depth. 

(c) For a uniform soil with a bulk density of 1.5 
gm. cm.? and an average moisture content of 20 per- 
cent over a depth interval of 1 foot above the water 
table, what depth of water in surface inches, when added 
to the ground water, will make the water table rise 1 
foot? Assume the particle density (real density) of 
the soil is 2.65 gm. cm.- 3 . In the right-hand nomogram 
of figure 8, place a straightedge on 1.5 of scale A, and 
on 2.65 of scale B,. Scale Ci then indicates a porosity 
of 0.44. Consequently, this soil when completely satu- 
rated will hold 0.44 ft. of water per foot of soil. In the 
left nomogram place a straightedge on 20 of scale Ai 
and 1.5 of scale B lB Scale C 2 then indicates that a 
moisture content of 20 percent corresponds to 0.3 ft. of 
water per foot of soil. Subtracting this from 0.44 indi- 
cates that 0.14 ft. of water per foot of soil, or (from 
scales Cj and C) 1.7 surface inches of water is suffi- 
cient to bring 1-ft. depth of this soil to saturation and 
hence to cause a rise of approximately 1 foot in the 
ground-water level. 

Field Leaching Trials 

Numerous field trials have demonstrated the effective- 
ness of leaching for salt removal. For example, Reeve 
and coworkers (1948) found that gypsiferous, saline- 
alkali soils in the Delta Area, Utah, are reclaimable by 
leaching with 4 ft. of water. The right-hand curve in 
figure 12 shows the salt distribution with depth at the 
beginning of leaching tests. This soil had been idle for 
many years, with the water table fluctuating between 
2 and 5 feet below the soil surface. Leaching treat- 
ments of 0, 1, 2, and 4 ft. of water were applied to test 
plots. The curves in the figure show the resulting 
change in salt content with depth. Wheat was planted 
and subsequently irrigated with 18 to 24 in. of water 
in 3 applications of 6 to 8 in. each. In addition, ap- 
proximately 12 in. of rain fell during the winter 
months, making a total of 30 to 36 in. of water applied 
in addition to the initial differential leaching treat- 
ments. The increase in yield of wheat was approxi- 
mately linear in relation to the depth of water used for 
leaching (fig. 13) . 



40 



AGRICULTURE HANDBOOK 60, U. S. DEPT. OF AGRICULTURE 



SOIL SURFACE 



2 FT. WATER 



UJ 
UJ 

u. 



I 2 



a. 

UJ 

a 




I FT. WATER 



NO WATER 




BEFORE LEACHING 



4 FT. WATER 



ELECTRICAL CONDUCTIVITY OF |:| EXTRACTS- MILLIMHOS/ CM. 
5 1.0 15 20 25 30 35 



43 



.2 .4 .6 .8 1.0 1.2 1.4 1.6 1.8 2.0 2.2 2.4 2.6 2.8 

PERCENT SALT 

Figure 12.-Distribution of salt content with depth as related to depth of water applied for leaching in the Delta Area, Utah (Reeve 

and others, 1948). 



Leaching practices, although basically the same, may 
vary from one region to another. In the Delta Area 
tests, the ponding method was used, and water was 
added in successive increments until the total amount 
for leaching had been applied. About 10 days were 
required to leach the plots with 4 ft. of water. I n some 
parts of the Imperial and Central Valleys of California, 
where infiltration rates are low, water is ponded on the 
surface by the contour-check method for periods up 
to 120 days. I n such i nstances, rice is someti mes grown 
to aid in the reclamation process and also to provide 
incomeduring leaching. Jn other areas, rice is included 
regularly in the crop rotation as an aid in salinity 
control . 

In addition to the removal of excess salts and ex- 
changeable sodium, other practices are usually required 
for complete reclamation. Plant nutrients that are 
leached from the soil must be replaced, and fertilizer 
practices following leaching should compensate for 
plant nutrient losses. Nitrogen is the principal nutri- 
ent subject to leaching loss. Soil structure that may 
have deteriorated during the salinization or alkaliza- 
tion process must be restored. Unfavorable soil struc- 
ture after leaching is sometimes a special problem and 
may be improved by adding manure or other forms of 
organic matter, by growing crops that are beneficial to 
structure, or by alternate wetting and drying, as indi- 
cated by the field tests of Reitemeier and associates 
(1948) and Bower and coworkers (1951). 



Special Practices for Salinity Control 

The failure to recognize that saline and alkali soils 
require special management practices can result in low 
production or in complete crop failure. These special 
practices can be followed over a period of time to 
improve lands that are partially affected or to prevent 
reclaimed lands from again becoming unproductive. 
Where only irrigation water of poor quality is avail- 
able or where drainage and full-scale reclamation are 
not economically feasible, it may be possible to carry 
on successfully what might be referred to as "saline 
agriculture." Irrigation, leaching, and tillage practices 
can all be directed toward salinity control. Salt-toler- 
ant crops can be selected and chemical amendments 
used when necessary. 

Many crop failures result from growing crops that 
have low salt tolerance. Alfalfa, barley, sugar beets, 
and cotton are tolerant crops that can often be grown 
where salinity is a problem. Lists of salt-tolerant 
fruits, vegetables, field, and forage crops are given in 
chapter 4. 

In general, irrigation methods and practices that 
provide uniformity of application and downward move- 
ment of water through soils favor salinity control. 
Methods that pond or flood water over the soil surface, 
such as border, check, and basin methods of irrigation, 
give greater uniformity of application than furrow or 
corrugation methods. Only part of the surface is cov- 



SALINE AND ALKALI SOILS 



41 



ered by water with the furrow and corrugation methods 
so that movement of water is downward and outward 
from the furrow and is upward into the ridges. Wad- 
leigh and Fireman (1949) have shown that by furrow 
irrigation excessive amounts of salts concentrate in the 
ridges. Salt distribution resulting from furrow irriga- 
tion in a test plot that was salinized initially to 0.2 
percent is shown in figure 14. They further showed that 
cotton plants in the ridges extracted moisture mainly 
from beneath the furrows where leaching occurred and 
that there was little root activity in the ridges. 

Germination and emergence of plants is often a criti- 
cal factor in over-all production. Ayers (1951) has 
shown that the germination of seeds is greatly retarded 
and that the number of seeds germinating may be ma- 
terially decreased by salinity. If favorable conditions 
can be maintained during the germination and seedling 
stages, certain crops may make fair growth even under 
moderately high salinity conditions. Heald and others 
(1950) conducted experiments in Washington on the 
preemergence irrigation of beets. They showed that 
irrigation next to the seed row caused movement of 
salts away from the seeds and into the ridges. Thie 
allowed the seeds to germinate and to become estab- 
lished in essentially nonsaline conditions, thereby in- 
creasing yield by increasing stand (fig. 15). Further 
over-all leaching increased sugar beet yields. 



Careful leveling of land makes possible more uni- 
form application of water and better salinity control. 
Barren spots that appear in otherwise productive fields 
are often the result of high spots that do not get sufficient 
water for good crop growth and likewise do not get 
sufficient water for leaching purposes. Lands that have 
been irrigated 1 or 2 years after leveling can often be 
improved by replaning. This removes the surface un- 
evenness caused by the settling of fill material. Annual 
crops should be grown following land leveling, so that 
replaning after 1 or 2 years of irrigation can be accom- 
plished without crop disturbance. 

Crusting of the soil and failure of seed lings to emerge 
may indicate an alkali condition that might be corrected 
by amendments. Irrigating more freqhently, especially 
during the germination and seedling stage, will tend to 
soften hard crusts and help to get a better stand. 

Drainage of Irrigated Lands in Relation to 

Salinity Control 

Drainage in agriculture is the process of removal of 
excess water from soil. Excess water discharged by 
flow over the soil surface is referred to as surface 
drainage, and flow through the soil is termed internal 
or subsurface drainage. The terms "artificial drain- 




LEACHING 



FEET OF WATER 



Figure 13.-Grain yields as related to the depth of water used for leaching in the Delta Area, Utah (Reeve and coworkers, 1948). 



259525 o- 54- 4 



42 



AGRICULTURE HANDBOOK 60, U. S. DEPT. OF AGRICULTURE 



PLANT 



STALK 




□ 



CONDUCTIVITY OF EXTRACT FROM SATURATED SOIL -MILLIMHOS/CM. 



Less than i.O 



l.O to 2.0 




2.0 to 5.0 



5.0 tO 6.0 



prinr^ 



Kv>3 10.0 to 50 




Above 50 



Figure 14. -Salt distribution under furrow-irrigated cotton for soil initially salinized to 0.2 percent salt and irrigated with water of 

medium salinity (Wadleigh and Fireman, 1949). 



age" and "natural drainage" indicate whether or not 
man has changed or influenced the drainage process. 

Irrigated land is drained primarily to increase agri- 
cultural productivity, but there are other beneficial 
effects. Areas that are poorly drained require the 
expenditure of large sums of money annually for con- 
struction of highway subgrades and for safeguarding 
public health, since mosquito control and other disease 
problems are related to drainage conditions. Drainage 
improvements serve many public and private interests, 
and the justification for drainage improvements should 
be based upon all benefits that may be derived 
therefrom. 

The drainage program for irrigated land should be 
initiated and continuously integrated with the develop- 
ment of the irrigation system in order to attain an effi- 
cient over-all water and salinity control program. The 
removal of excess water and salts must be considered in 
every irrigation enterprise. Excess water may be 
partially discharged or removed from the soil by natural 
means, but often supplementary drainage facilities are 
required. Irrigation practices, together with methods 
of distributing water, are related to drainage, and some- 
times the need for artificial drainage facilities may be 
lessened or avoided altogether by efficient management 
of irrigation water. 

The design of drainage systems is influenced by many 
factors, and there are no simple rules or formulas by 



which all of these factors can be taken into considera- 
tion. However, the principal factors can be grouped 
under drainage requirements, water-transmission prop- 
erties of soil, and boundary conditions. 

Drai nage Requi rements 

The permissible depth and mode of variation of the 
water table with respect to the soil surface and the 
quantity of water that a drainage system must convey, 
both surface and subsurface, relate to drainage design 
and may be referred to as the drainage requirements. 
The climate, the quality of the irrigation water, the 
characteristics of the soil, the crops, and the cropping 
system must all be considered in the determination of 
drainage requirements for any given locality. 

The adequacy of drainage for agricultural purposes 
depends upon whether or not there is an excess of water 
on or in the soil for periods of time that are detrimental 
to crops. Inadequate aeration of the soil may be a 
direct consequence of inadequate drainage and may 
result in a limitation of growth of plants or severe 
damage to root systems through pathological, physio- 
logical, or nutritional disturbances, or through limita- 
tion of the effective depth of the root zone. The opti- 
mum moisture content of the soil for tillage and other 
farming practices is also involved because farm opera- 
tions can be seriously delayed by wet soil. 



SALINE AND ALKALI SOILS 



43 



In irrigated regions the adequacy of drainage is re- 
lated to salinity. Salts in the irrigation water, in the 
soil, or in shallow ground waters increase the drainage 
requirements. In addition to aeration effects and soil- 
moisture requirements for tillage, a minimum allow- 
able water-table depth that will permit adequate leach- 
ing and that will prevent concentration of salts in the 
root zone by upward flow must be established. The 
depth to the water table must be such that upward flow 
of saline ground water into the root zone is reduced or 
eliminated. Thus, irrigation, leaching, and soil- 
management practices that are involved in the control 
of salinity are important in establishing drainage 
requirements. 

As a minimum requirement, a drainage system must 
be adequate to remove from the soil the equivalent 
depth of water that must be passed through the root 
zone in order to maintain a favorable salt balance. 
With a knowledge of the consumptive use, the mini mum 
amount of water required to be drained can be esti- 
mated by the use of equations 2 and 4: 



LR 



Z/fiw JJjKJ 



iw 



£>,„ EC. 



dw 



D lv =D cv +D, 



dw 



(2) 
(4) 



Equation 2 gives the fraction of the water applied as 
irrigation that must pass through and beyond the root 
zone to maintain the electrical conductivity of the drain- 
age water below a specified value (£C dw ) for the steady- 
state or long-time average salt-balance conditions. 
Equation 4 gives the depth of irrigation water (D iyv ) 
as a function of consumptive use (D^ w ) and the equiva- 
lent depth of drainage water (D dv/ ) . Solving equation 
2 for Z) iw , substituting in equation 4, and rearranging 
gives : 

Dtw^ y^Yji LR (8) 

Expressing LR in this equation in terms of the con- 
ductivity ratio of equation 2 gives: 

-Ed 



J-Jaw — 



^ 1 w 



dw 



^^dw — &C\w 



D 



cw 



(9) 



The depth of the water to be drained (D iw ) is thus 
expressed in terms of the electrical conductivity of the 
irrigation water and other conditions determined by the 
crop and climate; namely, consumptive use and salt 
tolerance of the crop. The salt tolerance of the crop 
is taken into account in the selection of permissible 
values of EC Aw . Equations 8 and 9 are subject to the 
assumptions made in deriving equation 2. 



AT THINNING TIME 

FOLLOWING 
PRE-EMERGENCE IRRIGATION 



AT MATURITY 

FOLLOWING 
NORMAL IRRIGATION 




-J 4 « 



22 



II 




RELATIVE SALT CONCENTRATIONS 



Very Low 



Y////////A Moderately High 



Low 



High 



Moderate 



:/:;:>; ':Wi Very High 



Figure 15.-Salt concentration in the vicinity of growing beets as related to position in the furrow (redrawn from Heald and others, 

1950). 



44 



AGRICULTURE HANDBOOK 6 0, U. S. DEPT. OF AGRICULTURE 



The term Z) dw in the equation does not include drain- 
age water that moves in-lateral ly from adjacent areas 
and that must pass into and through the drainage 
system, but represents only the depth by which irriga- 
tion water, assumed to be applied uniformly at the soil 
surface, exceeds the consumptive use. For any speci- 
fied £C dw , which depends upon the salt tolerance of the 
crop, the depth of drainage water ( D dw ) is the mini- 
mum depth of water that is required to be drained. 
This condition is satisfied when the previously defined 
leaching requirement is just met. For a value of 
£C dw = 8, which applies for moderately tolerant crops, 
and for irrigation waters of £C iw = 0.5, 1, 2, and 4 
mmhos/cm., the depths of drainage water that must 
pass through the soil are 7, 14, 33 f and 100 percent of 
the consumptive use(D cw ), respectively. 

The passage of excess water through the root zone is 
accompanied by a decrease in the electrical conductivity 
of the drainage water. The equivalent depth of drain- 
age water that is required to be drained (Z) dw )from soil 
where irrigation water is applied inefficiently but uni- 
formly may be estimated by substituting^ in equation 9 
the electrical conductivity of the drainage water (EC dw ) 
as sampled and measure-d from the bottom of the root 
zone. 

The depth of water that is drained beyond the root 
zone may also be expressed in terms of the water- 
application efficiency- and the total depth of water 
applied or the consumptive use. The equation 
£ = Z) 0W /D iw is based on the definition of water-appli- 
cation efficiency (Israelson, 1950), where E represents 
water-application efficiency and the other symbols are 
as previously defined. Solving this equation for D cw 
in one case and for D dw in the other, substituting in 
equation 4 and solving for J9 dw , we obtain: 



and 



Z> d w=0iw(l-£) 



D^ = D c J~-l\ 



(10) 



(11) 



Measured application efficiencies often run as low as 
25 percent and seldom exceed 80 percent. Correspond- 
ingly, the water to be drained that comes directly from 
irrigation will range from 20 to 75 percent of the 
irrigation water applied and from 25 to 300 percent 
of the consumptive use. The total quantity or equiva- 
lent depth of water to be drained will be equal to that 
given by these equations plus that from other sources, 
such as seepage from canals and artesian aquifers. 
Seepage from canals is a major source of excess ground 
water in many areas, and seepage losses of 30 to 50 
percent of the water diverted often occur. 

Water-Transmission Properties of Soils 

The principles and background theory for fluid flow 
in porous media are well known and are adequately 
treated in the literature. A discussion of the forces and 
properties determining the flow and distribution of 
water in soil, both saturated and unsaturated, and a 
description of measuring methods are given by Richards 



(1952) . An important part of this background theory 
is embodied in the well-known Darcy equation, which 
in its generalized form states that for isotropic media 
the flow velocity, or specific discharge, is proportional 
to the hydraulic gradient and is in the direction of the 
greatest rate of decrease of hydraulic head. 

The water-transmission properties of subsoils that 
cannot be controlled or changed appreciably have a 
direct bearing upon the design and layout of drainage 
systems. So'iLs, generally, are highly variable with 
respect to water-transmission properties, and it is neces- 
sary to assess the non homogeneity and to appraise the 
influence of soil variations on the direction and rate 
of flow of ground water. 

Boundary Conditions 

This concept is commonly used in the solution of 
flow problems and involves a geometric surface defin- 
ing the boundaries of the problem along with hydraulic 
conditions over this surface, i. e., hydraulic head, 
hydraulic gradient, and flow. In other words, the ex- 
ternal influences and constraints characterizing any 
given flow problem are included in the boundary con- 
ditions. While the root zone is the region of primary 
concern for agricultural drainage, a drainage problem 
may involve a considerably larger and deeper region. 
The upper and lateral bounding surfaces may be reason- 
ably definite, but the lower boundary will depend on 
stratigraphy and hydraulic conditions. Many irrigated 
areas of the West are in alluvial valleys where topog- 
raphy and stratigraphy vary widely and where there 
may be diverse sources of ground water. The identi- 
fication and delineation of these sources is especially 
important in establishing and defining boundary 
conditions. 

Surface drains function mostly to eliminate water 
from the soil surface that may otherwise contribute to 
underground flow. Deep gravity drains, tile, and open 
ditches provide outflow points below the ground sur- 
face for controlling water-table depths and hence are 
a part of the boundary conditions. They are mostly less 
than 15 ft. deep because of construction limitations. 
Where conditions are favorable for pumping, water 
tables can usually be maintained at greater depths and 
thereby be controlled more effectively by pumping than 
by any other method. Most wells are installed to ob- 
tain water for irrigation, but often they also function 
to improve drainage conditions. 

Layout and Placement of Drains 

Drainage systems may consist of intercepting drains 
or relief-type drains, depending upon their location and 
function. Intercepting drains collect and divert water 
before it reaches the land under consideration, and 
relief drains are placed to remove water from the land 
being drained. Pumped wells, tile, or open drains may 
serve either of these purposes. Relief-type drains are 
used in broad valleys where the land has little slope, 
whereas intercepting drains more often are used in 
areas where topography is irregular. In areas of roll- 



SALINE AND ALKALI SOILS 



45 



ing or irregular topography, where lands of appreciable 
slope are irrigated, water that percolates downward 
through the surface soil often flows laterally through 
subsoil materials in the direction of the land slope. 
In these areas, seeps may be caused by a decrease in 
grade, a decrease in soil permeability, a thinning out 
of permeable underlying layers, the occurrence of dikes 
or water barriers, or the outcropping of relatively im- 
permeable layers or hard pans. If the seepage water 
cannot be eliminated at its source, the placement of tile 
or open drains immediately above the seep to intercept 
such flows is usually the most effective procedure for 
solving this type of drainage problem. 

Proper placement of drains is of considerable im- 
portance in the design of a drainage system. In non- 
uniform soils drainage systems may best be designed 
by considering the nature and extent of subsoil layers 
and by locating the drains with respect to these subsoil 
materials. Generally drains should be oriented per- 
pendicular to the direction of ground-water flow and, 
where possible, should connect with sand and gravel 
layers or deposits. In soils of alluvial origin, the 
orientation of both permeable and impermeable de- 
posits may be such that a few well-placed drains may 
control ground water over a much larger area than the 
same length of drain installed with uniform spacing 
in accordance with some arbitrary pattern. This has 
been demonstrated in a number of irrigated areas. 
For example, in the Grand Valley, Colorado, open 
drains that cut across and intercept sand and gravel 
deposits provide much more effective drainage than 
drains dug parallel to these deposits. 

In areas where artesian conditions occur, drainage 
by tile and open drains is often impractical. Although 
the quantity of upward flow from an artesian source 
may be small, it usually exerts an important controlling 
effect on the height of the water table between drains. 
Artesian aquifers in many cases may be highly per- 
meable and ideally located for drainage purposes, but 
they may be unavailable for receiving and discharging 
excess water applied at the soil surface because of the 
artesian pressure condition. Reduction of the water 
pressure in these aquifers by pumping or other means 
should be a first consideration. 

The problem of flow into drains under falling water- 
table conditions has not been solved analytically. 
H owever, sol utions have been developed for the ponded 
condition where drains are installed in saturated 
isotropic soil with a layer of water covering the surface. 
The falling water-table case typifies the drainage con- 
ditions in irrigated soils where it is desired to maintain 
adequate depth of water table between drains, whereas 
the ponded area more nearly represents conditions in 
humid regions where it is desired to remove excess 
water in short time periods following precipitation. 
Although the falling water-table condition differs ap- 
preciably from the ponded case, some of the important 
findings with the ponded area may have useful applica- 
tion for the falling water-table condition. For the 
ponded case, assuming isotropic soil, Kirkham (1949) 
concluded that "The most important single geometrical 



factor governing rate of seepage of water from soil 
into drains is the drain depth. Doubling the depth of 
drains will nearly double the rate of flow." For the 
falling water-table case, which is the usual condition 
in arid regions, the depth to the water table midway 
between drains is directly dependent upon the depth 
of the drains. For a given spacing, assuming soil con- 
ditions do not change with depth and other conditions 
remain constant, the depth to water table midway be- 
tween drains increases directly with drain depth. 

Proximity of drains to relatively impermeable layers 
is also an important consideration. Kirkham (1948, 
p. 59) states: "Drains should not be placed too near, 
on, or in an impervious layer. ... it is found that 
lowering the drain onto or into an impervious layer, 
although increasing the hydraulic head, decreases the 
flow rate. ..." He further states that "Drain shape 
(as well as size) appears to be unimportant in govern- 
ing seepage rate into drains." From this, it is apparent 
that drain size should be determined primarily upon 
the basis of flow-velocity requirements. A gravel pack 
around tile drains is commonly used as a filter to allow 
freeflow of water and at the same time to prevent sedi- 
ment from entering the tile line. 

Techniques for Drainage Investigations 

A drainage investigation should provide information 
regarding the occurrence, flow, and disposition of excess 
water within a given basin or area. Information re- 
garding hydrology, geology, meteorology, topography, 
and soils is needed and for some areas is already rou ro- 
ll shed and available. Reports of earlier drainage^sur- 
veys should not be overlooked. 

Measurements of Hydraulic Head 

Inadequate drainage may be manifest by the pres- 
ence of ponded water, marshy lands, and the growth 
of hydrophytic plants; but, in the absence of these 
obvious signs, depth to ground water is the most com- 
mon index of the adequacy of drainage. Uncased 
observation wells are commonly used for determining 
the depth of the water table. Sometimes ground-water 
observation wells are lined with perforated casing. 
If there is a vertical component of flow, the true eleva- 
tion of the water table is difficult to determine unless 
piezometers are used. 

The water table is the elevation in the profile at 
which the soil water is at atmospheric pressure. This 
elevation corresponds to the bottom of the shallowest 
hole in which free water will collect. In a deeper hole 
or an observation well with perforated casing, the 
equilibrium elevation at which the water stands repre- 
sents a balance between inflow and outflow for all the 
soil layers penetrated by the hole and may not be a 
useful hydraulic- head value. 

The hydraulic head of ground water at each point in 
the soil is the elevation at which water stands in a riser 
connected to the point in question. There should be 
no leakage externally along such a riser or piezometer 
in order to insure that the elevation at which water 



46 



AGRICULTURE HANDBOOK 60, U. S. DEPT. OF AGRICULTURE 



stands in the piezometer is determined by the pressure 
in the ground water at the bottom end of the tube. 
This condition of external sealing is readily met under 
most field conditions for piezometers installed in ac- 
cordance with Methods 35a and 35b. Measurements 
of hydraulic head and hydraulic gradient provide basic 
information on drainage conditions and the source 
and flow of ground water. 

The number and arrangement of sites at which 
ground-water measurements should be made will de- 
pend upon the nature of the area in question and the 
purpose for which the measurements are made. In 
typical irrigated valleys information on both the ade- 
quacy of drainage and direction of ground-water flow 
is usually desired. Wells may be located to serve both 
purposes. Observation wells are often placed in a grid 
pattern for which spacing is selected to coincide with 
the land-survey system. In gently sloping areas, points 
of measurement can be farther apart than in areas of 
irregular topography. For determining the direction 
of the horizontal component of flow, water-table read- 
i ngs may be made at any desi red spaci ng. M ore meas- 
urement sites are required in localities where there are 
abrupt changes in the slope of the water table. 

Water-table contour maps and water-table isobath 
maps are useful in interpreting water-table data 
(Methods 36a and 36b). Profile flow patterns 
(Method 36c) may be used to show the nature of flow 
in cases where vertical as well as horizontal components 
of flow occur, such as sidehill seeps, seepage from 
canals, flow into drains, and upward flow from artesian 
aquifers. Water-table isopleths, which are described 
in Method 36d, can be used to show time fluctuations 
of the water table on a profile section. 

Convenient methods for installing small -diameter 
piezometers have been described by Christiansen 
(1943), Pillsbury and Christiansen (1947), and Reger 
and others (1950). Piezometers may be installed by 
either driving or jetting as outlined in Methods 35a 
and 35b. The jetting technique provides a log of the 
nature and arrangement of subsoil materials in addi- 
tion to the installation of a pipe for hydraulic- head 
readings. Piezometers 150 feet deep have been in- 
stalled by this method. 

Water levels in irrigation and domestic wells are 
often used for ground-water study. Water levels in 
such wells may or may not represent the water-table 
level. Deep-well readings should not be used as a 
measure of water table unless it can be definitely estab- 
lished by independent water-table measurements that 
the well reflects the true water-table level. Informa- 
tion regarding wells, such as total depth of well and 
depth of screens or perforations, is necessary in order 
to interpret well readings correctly. 

Determination of Subsoil Stratigraphy 

Hand augers, power augers, driven tubes, standard 
well-drilling equipment, and jetted piezometers can be 
used for studying subsoil materials and for locating 
and characterizing subsurface layers. The develop- 



ment of the jetting method of installing piezometers 
has made it possible to make subsoil investigations at 
only a fraction of the cost of augering or the use of 
well-drilling methods. Piezometers may be jetted for 
the sole purpose of determining subsoil stratigraphy, 
or the pipe may be left in place after the soil log is ob- 
tained as a permanent installation for hydraulic- head 
measurements. 

Subsoil logs from jetted piezometers are usually 
made on the basis of texture, since information on tex- 
ture provides an indication of the water-transmission 
properties of soils. Depths of strata changes may 
sometimes be obtained to within ±0.1 ft. by this 
method, and soil layers can be distinguished that are 
too thin to be logged by well-drilling methods. An 
estimate of the texture and consolidation of the mate- 
rial is made from the vibration or feel of the pipe to 
the hands during the downward motion, from the rate 
of downward progress, from the examination of sedi- 
ments carried by the effluent, and from the observation 
of color changes that occur in the effluent. (See 
Method 35b.) 

Standard well-drilling equipment may be used for 
obtaining samples of subsurface materials and for 
logging underground strata. Logs of irrigation, do- 
mestic, or municipal water-supply wells that have been 
drilled in an area may usually be found in either county 
or State governmental offices. Some States require 
well drillers to file with the State engineer a log of 
each well drilled. Such logs provide useful informa- 
tion regarding the major clay layers and principal 
water-bearing aquifers. They are often deficient in 
pertinent details, however, especially concerning sub- 
soil changes at shallow depths. In interpreting well 
logs the method of drilling should be taken into con- 
sideration. Logs of wells drilled by bailing methods, 
where sediments are actually obtained and examined 
from within a limited depth range, are usually more 
reliable than logs obtained by other drilling methods. 

Hand augers and driven tubes are generally limited 
to depths less than 20 ft. They are used mainly for 
appraising stratigraphy near the surface. Power 
augers of various types are commercially available 
that can be used to depths of 60 ft. or more. I n sandy 
soils it is sometimes necessary to case the hole with pipe 
or tubing as augering progresses in order to get a hole 
drilled to the desired depth and to obtain samples. 

Undisturbed cores, 4 in. in diameter and from depths 
up to 10 ft., can be obtained by use of the power-driven 
core-sampling machine, an earlier model of which has 
been described by Kelley and coworkers (1948). 
This machine is trailer mounted and is usable over 
terrain passable to trucks. Soil cores are useful for 
the observation of structure and for making various 
physical measurements on undisturbed subsoil mate- 
rials. Cracks, root holes, and fine sand lenticles may 
be overlooked with augering and other sampling 
methods, but these are preserved for examination in an 
undisturbed core. 



SALINE AND ALKALI SOILS 



47 



Determination of Water-Transmitting Properties 
of Soils 

In addition to determining the position and extent 
of subsoil materials as outlined above, information on 
the rates at which soils transmit water is required in 
planning and designing drainage systems. Soils are 
extremely variable with regard to water transmission. 
The heterogeneous nature in which most alluvial soils 
are deposited adds materially to the problem of assess- 
ing their water-transmitting properties. Soils formed 
both in place and by alluvial deposition may be ex- 
tremely variable not only in a lateral direction but with 
depth as well. The problem of appraising the water- 
transmitting properties of soils involves measurements 
by suitable methods at representative sites or on rep- 
resentative samples. 

The ratio of the waterflow velocity to the hydraulic 
gradient is called the hydraulic conductivity. This is 
the proportionality factor in the Darcy equation. This 
quantity varies over a range, as much as 100,000 
to 1, in earth materials in which drainage operations 
are conducted. Hydraulic conductivity is often re- 
lated to texture, coarse soils having high conductivity. 
Particle-size distribution may also be an important 
factor. Porous media with uniform particle sizes tend 
to be more permeable than materials having a more or 
less continuous range of sizes. 

The hydraulic conductivity of soils, although related 
in a general way to texture, depends also upon soil 
structure. Soils near the surface that may be dry 
much of the time and are subject to alternate wetting 
and drying, freezing and thawing, plant root action, 
and alteration by other biological processes may ex- 
hibit entirely different water-transmitting properties 
than soils of similar texture below a water table. From 
the standpoint of drainage the latter are of greater 
importance, since subsurface drainage is concerned 
largely with water movement below the water table. 

Hydraulic conductivity can be measured for dis- 
turbed samples or undisturbed cores in the laboratory 
or for undisturbed soil in the field. Measurements on 
disturbed samples of aquifer materials may be satis- 
factory for drainage investigation purposes, if the 
samples are packed to field density. Methods for 
making such measurements are summarized by Wenzel 
(1942). 

Several methods have been developed for measuring 
the hydraulic conductivity of soil in place in the field 
below a water table. A procedure developed by 
Diserens (1934) and Hooghoudt (1936) in Holland 
makes use of the rate of water seepage into an auger 
hole below the water table and is described in Method 
34d. The mathematical treatment developed by Kirk- 
ham and Van Bavel (1949) for this method assumes 
homogeneous isotropic soil, but hydraulic-conductivity 
determinations by this method in nonuniform soils may 
betaken as average or effective values. The auger-hole 
method is limited to soils below a water table in which 
the walls of the auger hole are stable. With the use of 



suitable screens it may also be used in sands or other 
noncohesive soils. 

The piezometer method, based on the analysis by 
Kirkham(1946), has been adapted for large diameter 
tubes by Frevert and Kirkham (1949) and for small 
diameter pipes by Luthin and Kirkham (1949). The 
latter procedure is particularly suitable for determining 
the hydraulic conductivity of individual layers of soil. 
It is essentially a cased auger hole in which an opening 
or cavity is placed at any desired depth in the soil, 
following the procedure outlined in Method 34c. 

Drainage design may be influenced by the fact that 
both uniform and nonuniform soils may be anisotropic 
with respect to hydraulic conductivity, i. e., the con- 
ductivity may vary with direction in the soil. Alternate 
lenses of coarse and fi ne sedi ments are commonly found 
in alluvial soils and usually conduct water more readily 
in a horizontal than a vertical direction. The above 
field methods may be useful in obtaining information 
on the degree to which soils are anisotropic. Reeve 
and Kirkham (1951) point out that field methods in 
which long cavities with respect to the diameter are 
used, such as is usually the case with both the auger- 
hole and the small-pipe piezometer methods, measure 
essentially the hydraulic conductivity in a horizontal 
direction, whereas the large-diameter tube method, 
which has a horizontal inflow surface, essentially 
measures conductivity for vertical flow. Hydraulic 
conductivity in any desired direction can be measured 
with undisturbed cores. 

Since most soils are not uniform, the problem of 
appraising the water-transmitting properties, as related 
to depth and spacing of drains, involves not only the 
method of measurement but also a statistical problem 
of sampling as well. The number of samples required 
for soil appraisal is increased if the soil is highly 
variable or if the samples are small in size. Reeve and 
Kirkham (1951) showed that the effective sizes of 
sample associated with a small core (2-in. diam. X 2 in. 
long), a piezometer (l-in. diam. X4-in. cavity), a tube 
(8-in. diam. with a cavity length equal to zero), and 
an auger hole (4-in. diam. X 30 in. deep), are in the 
ratio of 1, 35, 270, and 1,400, respectively; the latter 
three values being based on the region in which 80 
percent of the hydraulic- head difference is dissipated. 
It is apparent that field methods for appraising con- 
ductivity on large undisturbed volumes of soil have 
distinct advantages over laboratory methods. 

Information on the water conductance of subsurface 
aquifers often has application to drainage appraisal 
and can be obtained from well tests. High specific 
yield, i. e., high rate of flow per unit drawdown, indi- 
cates high aquifer permeability and vice versa. Data 
from existing wells can be used or new wells can be 
drilled. Wenzel (1942) has summarized and discussed 
the equations and methods used by a number of investi- 
gators of pumped wells. Theis (1935) presented equa- 
tions for flow into wells for nonequilibrium conditions, 
and Jacob (1940, 1947) reviewed the principles of flow 
in artesian aquifers. Peterson and coworkers (1952) 
have developed equations and procedures for study of 



48 



AGRICULTURE HANDBOOK 60, U. S. DEPT. OF AGRICULTURE 



ground-water flow to wells for the steady-state or 
equilibrium condition. 

Chemical Amendments for Replacement of 

Exchangeable Sodium 

The kind and amount of chemical amendment to be 
used for the replacement of exchangeable sodium in 
soils depend upon the soil characteristics, the desired 
rate of replacement and economic considerations. 

Suitability of Various Amendments Under 
Different Soil Conditions 

Chemical amendments that are applied to alkali 
soi I s are of three types: 



Amendments for alkali soils : 
Soluble calcium salts_ 

Acids or acid-farmers 



Calcium salts of low solubility. _. 
(May also contain magnesium) 



Chemicals 
Calcium chloride 
Gypsum 
Sulfur 

Sulfuric acid 
Iron sulfate 
Aluminum sulfate 
Lime-sulfur 
Ground limestone 
Byproduct lime from 
sugar factories 

While each type of amendment has a place in reclama- 
tion, effectiveness under different soil conditions is 
governed by several factors, the principal ones being 
the alkaline-earth carbonate content and the pH read- 
ing. From the standpoint of their response to the 
various types of amendments, alkali soils may be 
divided into three classes :( 1) Soils containing alkaline- 
earth carbonates, (2) soils having a pH reading greater 
than 7.5 but practically free of alkaline-earth carbon- 
ates, and (3) soils having a pH reading of less than 
7.5 and containing no alkaline-earth carbonates. 

Any of the soluble calcium salts, acids, or acid- 
formers may be used on soils in class 1, but limestone 
will be of no value. The addition of acid or acid- 
forming amendments to soils in classes 2 and 3 tends to 
make them acid in reaction. When the amount of acid 
or acid-forming amendment needed for reclamation is 
sufficient to make the soil excessively acid, the choice 
of amendment is limited to soluble calcium salts, unless 
limestone also is applied. In general the acidification 
of soils of arid regions to a pH reading as low as 6 to 
6.5 is usually beneficial to plant growth. To determine 
if the amount of acid or acid-former needed for recla- 
mation is sufficient to cause excess acidity, the amend- 
ment can be applied at the desired rate to a sample of 
the soil and a pH reading can be obtained after the 
reaction is complete. If the addition of sulfur, which 
reacts slowly in the soil, is contemplated, the addition 
of a chemically equivalent amount of sulfuric acid may 
be useful to predict the pH reading that may eventually 
be obtained upon complete oxidation of the sulfur. 
While the application of limestone alone to soils of 
classes 2 and 3 will tend to be beneficial, the effective- 
ness of lime on different soils varies markedly, inas- 
much as the solubility of CaC0 3 decreases with in- 
creasing pH reading. Data on CaC0 3 solubility in 



relation to pH reading are given by De Sigmond (1938) 
as follows : 

Solubility of CaC0 3 
pH value of CaCOa saturated solution : (Meq./l.) 

6.21 19.3 

6.50 14.4 

7.12 7 . 1 

7.85 2 . 7 

8.60 1 . 1 

9.20 . 82 

10.12 .36 

Sodium carbonate or carbon dioxide was used to ob- 
tain pH readings above or below 7. On the basis of 
these data it is apparent that the effectiveness of lime- 
stone as an amendment is markedly decreased at pH 
readings above 7.5, whereas it may be quite effective at 
pH readings below 7. Hence, limestone may be used 
to advantage on class 3 soils, but its value on class 2 
soils is questionable. Some soils that contain excess 
exchangeable sodium also contain appreciable ex- 
changeable hydrogen and, therefore, have an acid 
reaction. In Hungary large areas of such soils have 
been quickly and effectively reclaimed by the addition 
of chalk (CaC0 3 ). 

Chemical Reactions of Various Amendments in 

Alkali Soils 

The following chemical equations illustrate the man- 
ner in which various amendments react in the different 
classes of alkali soils. In these equations the letter X 
represents the soi I exchange complex. 

Class 2. Soils Containing Alkaline-Earth Car- 
bonates 

Gypsum.— 2NaX + CaS0 4 ^±CaX 2 + Na 2 S0 4 

Sulfur.- 

( l) 2S-f 30 2 ^2SO 3 (microbiological oxida- 
tion) 

(2) SO,+H 2 0^±rLS0 4 

(3) H 2 S0 4 + CaCO s ^CaS0 4 + C0 2 + Ho0 8 

(4) 2N aX + CaS0 4 ;=±CaX 2 +Na 2 S0 4 

Lime-sulfur (calcium POLYSULFIDE ) . — 

( 1) CaS 5 + 80, + 4H 2 O^CaS0 4 + 4H 2 S0 4 

(2) H 2 S0 4 + CaCO^CaS0 4 + C0 2 + H 2 8 

(3) 2NaX+CaS0 4 ^CaX,Na 2 S0 4 

IRON SULFATE. 

( 1) FeS0 4 + H,O^H 2 S0 4 + FeO 

(2) H 2 S0 4 + CaC0 3 ^CaS0 4 + COo + Ho0 8 

(3) 2NaX+CaS0 4 ^±CaX 2 +Na 2 S0 4 



8 The reaction of H 2 S0 4 and CaC0 3 may also be written as 
follows: H 3 S0 4 +2CaCO,,^CaS0 4 +Ca(HC0 3 ) 2 . Under these 
conditions the Ca (HCCMs as well as the CaS0 4 would be 
available for reaction with exchangeable sodium and 1 atom of 
sulfur when oxidized to H 2 S0 4 could theoretically result in the 
replacement of 4 sodium ions by calcium. Kelley (1951, p. 135) 
found under field conditions that approximately 3 exchangeable 
sodium ions per atom of sulfur were replaced, whereas a green- 
house-pot experiment conducted at this Laboratory indicated 
that the reaction takes place without the formation of appre- 



SALINE AND ALKALI SOILS 



49 



Class 2. Soils Containing No Alkaline-Earth Car- 
bonates; pH 7.5 or Higher 

G ypsu m .-Same as in class 1. 

SULFUR.-Steps ( 1) and (2) as in class 1. 

(3) 2NaX+H 2 S0 4 ^±2HJ + Na 2 S0 4 

LIME-SULFUR.-Step (1) as in class 1. 

(2) 10NaJ + 4H 2 SO 4 + CaSO 4 ^8HZ + CaZ 2 + 
5Na 2 S0 4 

Iron SULFATE.-Step (1) as in class 1. 

(2) 2NaX +H 2 S0 4 ^2HZ+Na 2 S0 4 

Li m eston e .-Two possibilities suggested by Kelley 
and Brown (1934) are: 

(1) 2NaX +CaC0 3 ?=±CaZ 2 +Na 2 CO. 

(1) NaZ+HOH^±NaOH + HZ 

(2) 2HZ-hCaC0 3 ^±CaZ-f C0 2 + H 2 

Class 3. Soils Containing No Alkaline-Earth 
Carbonates; pH Less Than 7.5 

Gypsum. — Same as in class 1 and 2. 

SULFUR.-Sameasin class 2. 

LIME-SULFUR.-Sameas in class 2. 

IRON SULFATE.-Same as in class 2. 

LIMESTONE.-Sameasin class 2, and if exchange- 
able hydrogen is present: 

(1) 2HX + CaC0 3 ^CaZ 2 + C0 2 + H 2 

Estimation of Amounts of Various Amendments 
Needed for Exchangeable-Sodium Replace- 
ment 

/Exchangeable sodium and cation-exchange-capacity 
determinations serve as valuable guides for estimating 
the amounts of chemical amendments needed to reduce 
the exchangeable-sodium-percentages of alkali soils to 
given levels. The procedure for estimating the amount 
of amendment needed for a given set of conditions can 
be illustrated by an example. Suppose the to 12-in. 
layer of an alkali soil contains 4 meq. of exchangeable 
sodium per 100 gm. and has a cation-exchange-capacity 
of 10 meq. per 100 gm. The exchangeable-sodium- 
percentage is therefore 40. It is desired to reduce the 
exchangeable-sodium-percentage to about 10. This will 
necessitate the replacement of 3 meq. of exchangeable 
sodium per 100 gm. Assuming quantitative replace- 
ment it will be necessary to apply the amendment at 
the rate of 3 meq. per 100 gm. of soil. By referring to 
table 6, which relates tons of gypsum and sulfur per 
acre-foot of soil to milliequivalents of sodium per 100 
gm. of soil, it is found that 5.2 tons of gypsum or 0.96 
ton of sulfur are required. If it is desired to use 
amendments other than gypsum or sulfur, the supple- 

ciable amounts of Ca(HC0 3 ) 2 . A high soil-moisture level, low 
soil temperatures, and the reiease of C0 2 by plant roots would 
favor the formation of Ca (HC0 3 ) 2 as a product of the reaction. 



mentary data given below will be helpful in converting 
the tons of sulfur found to be needed in table 6 to tons 
of other amendments. 

Tons equivalent to 1 
Amendment : ton of sulfur 
Sulfur 1. 00 

Lime-sulfur solution, 24 percent sulfur 4.17 

Sulfuric acid_ ._"________"-_ 3.06 

Gypsum (CaS0 4 2H 2 0) 5.38 

Iron sulfate (FeS0 4 -7H,0> 8.69 

Aluminum sulfate (AUSOJa 18H 2 0) 6.94 

Limestone (CaC0 3 ) 3.13 

Table 6. — Amounts of gypsum and sulfur required 
to replace indicated amounts of exchangeable sodium 



Exchange- 










able sodium 
(Meq. per 


Gypsum 1 
(CaSCV 


Gypsum i 
(CaSCV 


Sulfur 


Sulfur 

/ c \ 


100 gm. of 


2H 2 0) 


2H 2 0) 


(S) 


(S) 


soil) 












Tons 1 acre- 


Tons / acre- 


Tons 1 acre~ 


Tons/a cre- 




foot! 


6 inches3 


foot 2 


6 inches 3 


1 


1.7 


0.9 


0.32 


0. 16 


2 


3.4 


1.7 


.64 


.32 


3 


5.2 


2.6 


.96 


.48 


4 


6.9 


3.4 


1.28 


.64 


5 


8:6 


4.3 


1.60 


.80 


6 


ID. 3 


5.2 


1.92 


.96 


7 


12.0 


6.0 


2.24 


1. 12 


8 


13.7 


6:9 


2.56 


1.28 


9 


15.5 


7.7 


2.88 


1.44 


10 


17. 2 


8.6 


3.20 


1.60 



1 The amounts of gypsum are given to the nearest 0.1 ton. 
2 1 acre-foot of soil weighs approximately 4,000,000 pounds. 
3 1 acre-6 inches of soil weighs approximately 2,000,000 
pounds. 

The reaction between an amendment such as gypsum 
and exchangeable sodium is an equilibrium reaction 
and, therefore, does not go entirely to completion. 
The extent to which the reaction goes to completion is 
determined by the interaction of several factors, among 
which are the differences in the replacement energies 
of calcium and sodium, the exchangeable-sodium- 
percentage, and the total cation concentration of the 
soil solution. For the usual case where a quantity of 
gypsum equivalent to the amount of exchangeable 
sodium present in the surface 6- or 12-in. layer of soil 
is applied, some progress has been made in determining 
the percentage of the applied calcium that reacts with 
exchangeable sodium. The available data indicate that 
when the exchangeable-sodium-percentage of the soil 
exceeds 25, 90 percent or more of the calcium supplied 
bv the amendment replaces exchangeable sodium as the 
soil is leached. The percentage of added calcium that 
replaces exchangeable sodium does not become less 
than 50 until the exchangeable-sodium-percentage be- 
comes less than 10. It should be pointed out that under 
the above conditions not all of the replacement of ex- 
changeable sodium takes place in the depth of soil upon 
which the application is based, although the greater 
part of it does. As a general rule, it is suggested that 



50 



AGRICULTURE HANDBOOK 60, U. S. DEPT. OF AGRICULTURE 



the rates of gypsum and sulfur application indicated by 
table 6 be multiplied by the factor 1.25 to compensate 
for the lack of quantitative replacement. 

A simple test based on the work of McGeorge and 
Breazeale (1951) has been proposed by Schoonover for 
determining the gypsum requirement' of alkali soils. 
The test, which is given as Method 22d, involves an 
arbitrary procedure and does not measure a distinct 
chemical property of the soil. The relation between 
the exchangeable-sodium content and the gypsum re- 
quirement as determined by Method 22d, of 29 non- 
gypsiferous soil samples has been studied at the 
Laboratory. The ranges in various characteristics of 
the samples were as follows: electrical conductivity 
of the saturation extract, 0.2 to 30 mmhos/ cm.; ex- 
changeable-sodium-percentage, 6.3 to 65.5 ; and ex- 
changeable-potassium-percentage, 2.1 to 27.3. As in- 
dicated by a correlation coefficient of 0.96, a good 
relation was found between exchangeable-sodium con- 
tent and gypsum requirement. For soil samples hav- 
ing exchangeable-sodium contents ranging from 0.1 to 
12 meq./lOO gm., the relation between the two vari- 
ables is expressed by the equation: Exchangeable 
sodium, milliequivalents/100 gm. = 0.96 + 0.99 X gyp- 
sum requirement, imlliequivalents/lOOgm. 9 Inasmuch 
as Method 22d gives a good estimate of the exchange- 
able-sodium content of these alkali soils, it would ap- 
pear to be useful for estimating the amount of gypsum 
needed when information on the exchangeable-sodium 
content and the cation-exchange-capacity is not other- 
wise available. Amounts of gypsum can be converted 
to quantities of other chemical amendments by the use 
of table 6 and data on page 49. 

Speed of Reaction of Amendments and Economic 

Considerations 

The choice of a chemical amendment may be in- 
fl uenced by the ti me requi red for its reaction i n the soi I . 
I n general, the cheaper amendments are slower to react. 
Consequently, if immediate replacement of exchange- 
able sodium is desired, one of the quicker acting but 
more expensive amendments will be needed. 

Owing to its high solubility in water, calcium 
chloride is probably the most readily available source of 
soluble calcium, but it is seldom used because of its 
cost. Sulfuric acid and iron and aluminum sulfates 
that hydrolyze readily in the soil to form sulfuric acid 



ALKALI 



9 Schoonover, W. R. examination of soils for 
University of California Extension Service, Berkeley, Califor- 
nia. 1952. [Mimeographed.] 

In a private communication, C. D. Moodie of the Washington 
Agricultural Experiment Station has reported a study of the 
relation between the gypsum requirement and the exchangeable- 
sodium contents of soils from the Yakima Valley, Washington. 
A relation similar to that obtained by Schoonover was obtained 
for soils containing low amounts of exchangeable potassium, but 
for soils containing high amounts of exchangeable potassium 
the slope of the regression line was considerably lower. Thus, 
estimates of the exchangeable-sodium content based on the 
gypsum requirement and the equation given in this handbook 
may be high if the soil contains large amounts of exchangeable 
potassium. 



are also quick-acting amendments. Sulfuric acid is 
often cheap enough for field application, but the use of 
iron and aluminum sulfates usually is not economically 
feasible. Because of their relatively low cost, gypsum 
and sulfur are the most common amendments used for 
reclamation. The rate of reaction of gypsum in replac- 
ing sodium is limited only by its solubility in water; 
its solubility is about 0.25 percent at ordinary tempera- 
tures. The presence of sodium and chloride ions in the 
water increases the solubility of gypsum, whereas cal- 
cium and sulfate ions tend to decrease its solubility. 
Limited data indicate that the application of 3 to 4 ft. 
of irrigation water is sufficient to dissolve 4 or 5 
tons/acre of agricultural gypsum having a degree of 
fineness such that 85 percent will pass a 100-mesh 
sieve. 

As sulfur must first be oxidized by microbial action 
to the sulfate form to be available for reaction, it is 
usually classed as a slow-acting amendment. McGeorge 
and Greene (1935) have shown in laboratory studies 
of Arizona soils that sulfur applications of about 1 
ton/ acre are rapidly and usually completely oxidized 
in 2 or 3 weeks under favorable moisture and tempera- 
ture conditions. Larger applications required more 
time for complete oxidation. They also found that 
within the usual particle-size limits of agricultural 
sulfur, the coarse-grade material was practically as 
effective as the finer and more expensive grades. In 
spite of these findings, various agriculturists frequently 
report incomplete oxidation of sulfur in soils a year 
or more after application. Often this appears to be 
caused by the presence of lumps of the sulfur and in- 
sufficient mixing of the amendment with the soil fol- 
lowing application. 

As previously mentioned, the solubility of limestone 
when applied to alkali soils is markedly influenced by 
thepH reading and by the presence of exchangeable 
hydrogen. Unless the soil is decidedly acid, the chemi- 
cal reaction of limestone is slow. Particle size is also 
an important factor affecting the rate at which lime- 
stone, gypsum, and sulfur react in soils. The finer the 
particle size the more rapid the reaction. 

There is considerable interest at present in the use 
of lime-sulfur as an amendment. Lime-sulfur is a 
brown, highly alkaline liquid containing calcium 
polysulfides and some calcium thiosulfate. The cal- 
cium content is ordinarily about one-fourth that of the 
sulfur content, and its action depends mostly on the 
sulfur content. Usually the material is applied in irri- 
gation water. Like elemental sulfur, it must first be 
oxidized to sulfuric acid and then react with alkaline- 
earth carbonates to produce a soluble form of calcium. 

Application of Amendments 

From the standpoint of efficiency in replacing ex- 
changeable sodium, it is advantageous to leach most of 
the soluble salts out of the soil before applying chemi- 
cal amendments. As a result of the removal of soluble 
salts, a higher proportion of the calcium supplied by 
the addition of amendments is adsorbed by the soil- 



SALINE AND ALKALI SOILS 



51 



exchange complex. The advantage gained through in- 
creased efficiency in exchangeable-sodium replacement 
by leaching prior to the application of amendments 
may be more than offset by the decrease in soil 
permeability that usually accompanies the leaching of 
saline-alkali soil. Whether amendments should be ap- 
plied before or after removal of soluble salts, therefore, 
will depend upon permeability relationships. 

Such chemical amendments as gypsum, sulfur, and 
limestone are normally applied broadcast and then in- 
corporated with the soil by means of a disk or plow. 
Thorough incorporation is especially important when 
sulfur is used to insure rapid oxidation to the sulfate 
form. Because of hazards in handling, the application 
of suituric acid is difficult under ordinary field condi- 
tions. However, special equipment is now available 
that sprays the concentrated acid on the soil surface. 
Although chemical amendments are ordinarily applied 
to the surface, deeper placement may be advantageous 
if the exchangeable-sodium accumulation occurs uni- 
formly in the subsoil, or B horizon. While there ap- 
pears to be no information on the subject, it is possible 
to obtain deep placement by distributing the amendment 
behind a plow or subsoiler. 

Amendments are sometimes applied in the irrigation 
water. Special equipment for treating irrigation waters 
with gypsum has been described by Fullmer (1950). 
A simple method of treatment consists in placing a bag 
of gypsum with the side slit open in the irrigation ditch, 
preferably at a weir where the water has considerable 
turbulence. 

Except where sulfur is used, saline-alkali soils 
should be leached immediately following the applica- 
tion of amendments. Leaching dissolves and carries 
the amendment downward, and it also removes the 
soluble sodium salts that form as a result of cation ex- 
change. Sails receiving sulfur ordinarily should not be 
leached until sufficient time has been allowed for most 
of the sulfur to oxidize and form gypsum, but the soils 
should be kept moist, as moisture is essential to the 
process of microbial oxidation. 

Improvement of the physical condition of alkali 
soils involves the rearrangement and aggregation of 
soil particles as well as the replacement of exchangeable 
sodium. This has been demonstrated and emphasized 
by Gardner (1945). The rearrangement of soil par- 
ticles so as to improve physical condition is facilitated 
by alternate wetting and drying, by alternate freezing 
and thawing, and by the action of plant roots. 

Laboratory and Greenhouse Tests as Aids 

to Diagnosis 

While physical and chemical analyses made on saline 
and alkali soil samples provide basic data that may be 
needed to ascertain the cause of low productivity and 
the treatments required for reclamation, supplementary 
tests conducted on soil columns or in greenhouse pots 
are often helpful in obtaining satisfactory answers to 
soil problems. Such tests may be used to verify con- 
clusions reached on the basis of physical and chemical 



tests or to check on how the soil responds to indicated 
treatments for improvement. It should be recognized, 
however, that plant growth on saline and alkali soils 
contained in small pots may beat variance with growth 
obtained under field conditions. Laboratory and 
greenhouse tests are less costly, less laborious, and less 
time-consuming than field tests and often provide valu- 
able clues as to the behavior of the soil in the field. 
Generally, all but the more promising procedures for 
improving saline and alkali soils can be eliminated by 
laboratory and greenhouse studies. 

Laboratory tests on soil columns may be used to esti- 
mate the amount of leaching needed for removal of ex- 
cess soluble salts; to determine the response of soils 
to the addition of various kinds and amounts of amend- 
ments; and to determine the changes in such soil prop- 
erties as permeability, pH reading, and exchangeable- 
sodium- percentage that take place upon leaching. De- 
terminations on soil columns are especially useful in 
the diagnosis of saline-alkali soils, as the characteristics 
of these soils usually change markedly upon being 
leached. 

It would be best to conduct tests on undisturbed soil 
cores. A power-driven soil sampler capable of taking 
4-inch diameter cores to a depth of 10 feet has been 
developed by Kelley and associates (1948). In the 
absence of a core sampler, disturbed samples repre- 
senting the various soil layers may be packed in tubes 
of convenient diameter and length. A technique similar 
to that used for making hydraulic-conductivity meas- 
urements on disturbed soil samples can be used in 
setting up these soil columns. Leaching and amend- 
ment treatments may then be applied to the soil 
columns, and the effects upon water- movement rates 
noted. Changes in soluble-salt content, pH reading, 
and exchangeable-sodium status obtained by various 
treatments may be determined by removing the treated 
soil from the tube and making the appropriate 
analyses. 

Greenhouse tests are useful when it is desired to ob- 
tain information on plant-growth responses. They 
may be used for various purposes such as to determine 
whether the soil contains sufficient soluble salt or ex- 
changeable sodium to affect plant growth adversely, to 
determine plant response to leaching and the addition 
of chemical amendments, and to estimate the fertilizer 
needs of saline and alkali soils (Bower and Turk, 1946). 

Greenhouse pot tests may be conducted under vari- 
ous conditions. The procedure to be followed will 
depend upon the facilities available, the kind of plant 
to be grown, and the purpose of the tests, a few sug- 
gestions for conducting greenhouse tests are: 

(a) If possible, use the crop or crops to be grown 
in the field. 

(b) Use containers of soil as large as feasible. I f 
leaching treatments are to be employed, pro- 
vision should be made for measuring the 
volume and salt content of the leachate. 

(c) An attempt should be made to grow the crop 
during its normal season and to avoid exces- 



52 



AGRICULTURE HANDBOOK 60, U. S. DEPT. OF AGRICULTURE 



sive temperatures that are often obtained 
under greenhouse conditions. 

(d) Replicate each treatment at least twice and 
arrange each set of treatments in randomized 
blocks. 

(e) If possible, irrigate with water having the 
same composition as that to be used in the 
field. 

(/) If the soil has been leached or amendments 
applied, it may be desirable to analyze the 
soil at the conclusion of the test to determine 
the changes in the soil properties that have 
taken place. 

Although this handbook is not primarily concerned 
with soil fertility, it should be recognized that saline 
and alkali soils, like other soils of arid regions, usually 
respond markedly to nitrogen and phosphorus fertiliza- 
tion. Adequate fertilization after the removal of excess 
soluble salts and exchangeable sodium is usually re- 
quired to obtain maximum productivity. The green- 
house technique devised by Jenny and coworkers 
(1950) for determining nutrient level and fertilizer re- 
sponse is suggested as a possible method for determin- 
ing the fertilizer requirements of saline and alkali 
soils. 

Reclamation Tests in the Field 

Leaching operations and the application of amend- 
ments in the field usually entail considerable expense. 
Therefore, before attempting the improvement of saline 
and alkali soils on a large scale, it is frequently desir- 
able to determine whether a proposed treatment will 
be successful. Often this can be ascertained on an ex- 
perimental basis by the use of field plots. It is not the 
purpose of this section to give methods for conducting 
field-plot experiments of the research type. However, 
procedures are given that are considered adequate for 
testing treatments involving leaching, cultural prac- 
tices, and the application of amendments. Tests in 
which drainage is a treatment are difficult to conduct on 
a plot basis and, hence, will not be considered. 

Saline and alkali soils usually are extremely variable 
in nature, their characteristics often changing-markedly 
over relatively short distances. Therefore, considerable 
care should be taken to select a test area that is as uni- 
form as possible and yet representative of the soils to be 
considered. Examination and tests of soil samples 
from various locations over the proposed test area-are 
valuable in determining soil uniformity. Sometimes it 
is difficult to locate a single area of sufficient size and 
uniformity to conduct the test. Then it is advisable to 
place individual replications on separate areas within 
the field. 

Selection of the size and shape of plots is influenced 
by the kinds of treatments to be used, the crop to be 
grown, the method of applying water, and the amount 
of space needed for the operation of equipment. Ordi- 
narily, the plots should be as small as possible, as this 
tends to reduce soil variability within the test area. If 
at all feasible, a border or dike should be constructed 



around each plot to control the application of water. 
This permits the impounding of water for leaching and 
the estimation of infiltration rates. Tests that involve 
only the application of amendments such as gypsum or 
manure may be conducted on plots as small as 15 ft. 
by 15 ft. On such plots, the amendments can be ap- 
plied by hand. When leaching is a differential treat- 
ment, plots of somewhat larger size are needed, as 
border effects may be of considerable magnitude in 
small plots. Leachig tests have been satisfactorily 
conducted on % -acre plots. Cultural treatments, such 
as subsoiling and deep plowing, may require the use of 
fairly large plots to permit operation of the machinery. 
From the standpoint of minimizing border effects, plots 
should be as nearly square as possible. Square plots 
are usually convenient to handle when the land is 
flood -irrigated, but when the slope of the land is such 
that water must be applied in furrows or corrugations 
a long narrow plot must be used. Cropping procedure 
and tillage operations must also be considered in select- 
ing the shape of the plot. 

The design of field-plot tests is governed primarily 
by the treatments to be used (fig. 16). The simplest 
design is that in which the various treatments are ar- 
ranged in blocks and located at random, each treatment 
occurring only once in each block. Individual blocks 
serve as replications. This design is satisfactory for 
comparing various amendments or cultural practices or 
for testing the effect of leaching. If the test involves a 
combination of amendments and leaching or cultural 
treatments, it is advantageous to employ a split-plot 
design in which leaching or cultural treatments consti- 
tute main plots and the amendment treatments consist 
of subplots. Owing to the marked variability of saline 
and alkali soils, it is recommended that treatments be 
replicated at least four times. All treatments within 
each replicate block should be located at random. 

The improvement of saline and alkali soils may be 
evaluated by means of plant-growth responses, soil 
analyses, and determinations such as infiltration rate. 
When the problem is one of excess salinity only, deter- 
minations of crop yields on the various plots often 
will suffice for the evaluation of the treatments. If 
facilities are available, it is also advisable to determine 
by analysis the soluble-salt content of the soil before 
and after treatment. In alkali soils where poor physi- 
cal condition is a problem, the effect of the treatments 
upon the soil as well as upon plant growth should be 
determined. Changes in the exchangeable-sodium con- 
tent of the soil upon treatment may be determined by 
soil analyses, whereas improvement in water-transmis- 
sion properties may be estimated by means of infiltra- 
tion measurements. Estimates of infiltration rates are 
readily obtained when individual plots are flood-irri- 
gated. Infiltration rates on furrow -irrigated plots may 
be estimated by measuring the amount of water applied 
to the plot and the amount that runs off. 

Applications of chemical amendments influence both 
the physical and chemical properties of alkali soils. 
In studying the response of plants on alkali soils to the 
application of chemical amendments, it may be desir- 



SALINE AND ALKALI SOILS 



53 



LEACHING OR CULTURAL TREATMENTS 
( BASIN IRRIGATION ) 



AMENDMENT TREATMENTS 
( BASIN IRRIGATION ) 



L 2 or C 2 



L 4 or C 4 



30' 



■*l 



L 3 or C 3 



L ( or C| 



T 

-o 

to 



-\ 


15' 








\ 


A 5 


A 7 


A . 


A 3 


io 


A 2 


A 4 


A 6 


A 8 



} 



COMBINATION OF AMENDMENT AND 
LEACHING OR CULTURAL TREATMENTS 

( BASIN IRRIGATION ) 



CULTURAL OR AMENDMENT 
TREATMENTS 
(FURROW IRRIGATION ) 




30' 



"*1 



•"2 

or 



•-4 
or 



T 



A 2 I A 4 



Al I 






A3 



2 

+ 



_ A 3 j A 4 

it 
I A 



A2 



I 



I 



A 4 | A 3 
A, | A 2 



15' 



T 



IO 



To L. 



__ or 
C l 



J 











-is 1 * 


C| 


C 5 


C 3 


C 2 


C 4 


or 


or 


or 


or 


or 


A i 


A 5 


A 3 


A 2 


A 4 



Figure 16. -Example showing individual replicates of plot layouts for conducting field tests: C, Cultural treatments; L, leaching 
treatments; A, amendment treatments; main plot boundary; subplot boundary. The subscripts refer to treat- 
ment levels, for example: Li, control; L 2 , 12 surface inches; L»,36 surface inches. 



54 



AGRICULTURE HANDBOOK 60, U. S. DEPT. OF AGRICULTURE 



able to separate the strictly chemical aspects of 'the 
response from the physical aspects. Preliminary tests 
indicate that treatment of alkali soils with the recently 
developed commercial aggregating agents will largely 
eliminate poor physical condition without altering the 
chemical characteristics appreciably. Therefore, recla- 
mation tests that include applications of chemical 
amendments and commercial aggregating agents singly 
as well as in combination are suggested as a means for 
determining the nature of the response. 

Reclamation of Saline and Alkali Soils in 

Humid Regions 

This chapter deals primarily with the improvement 
and management of saline and alkali soils as they occur 
in the arid and semiarid regions of western United 
States. Any treatment of the subject would be incom- 
plete, however, without reference to the pioneer re- 
search work and the extensive practical experience with 
the reclamation of saline and alkali soils in the Nether- 
lands and other low countries in humid regions. Un- 
derlying principles relating to soil properties and plant 
responses apply equally well to both cases. The main 
difference is that in humid climates precipitation ex- 
ceeds consumptive use, so that if drainage is adequate, 
i. e., if the water table is maintained at a sufficient 
depth, excess soluble salts are leached out of the soil 
by rain water. 

It often happens that the rainfall pattern in humid 
climates during the crop growing season is not ideal 
and it is profitable to maintain the water table at some 
elevation that is in or near the root zone. Subirrigation 
is hazardous in arid regions, but it is a relatively com- 
mon practice in humid climates. In any climate this 
practice requires close attention to the concentration of 
soluble salts in the root zone, and careful coordination 
between subirrigation, leaching, and drainage require- 
ments. Hooghoudt (1952) has recently reviewed the 
methods and practices used in the Netherlands for tile 
drainage and subirrigation. 

A special case of salinity in humid as well as arid 
climates occurs in greenhouse soils. This type of agri- 
culture has considerable economic importance in many 
countries. Since crop production is directly dependent 
on irrigation and the leaching action of rainfall is 
absent, water management to control salinity and ex- 
changeable sodium in the soil is the same as for irriga- 
tion agriculture in an arid climate. 

Economically, in humid climates the most important 
consideration of soil salinity and exchangeable sodium 
has been in connection with the drainage and reclama- 
tion of soils underlying salty lakes and shallow coastal 
waters. In the Netherlands, experience with this 
process extends over many centuries, and the large 



areas of fertile agricultural land that have been gained 
by this means have become a major factor in the na- 
tional economy. Zuur (1952) has sketched historical 
and technical aspects and has given an introduction to 
the extensive literature of the Netherlands on this sub- 
ject. He states that, to start with, soils reclaimed from 
the sea contain about 2 percent sodium chloride. In 
2 years after ditching, this content is reduced "in the 
wet Dutch climate" to 0.1 percent or less in the surface 
80 cm. of sandy soils. Clay soils require a longer time 
to leach to this depth, but crops can be grown fairly 
soon after artificial drainage is established. 

Most of the polder soils of the Netherlands, coming 
both from recent marine deposits and from old sea 
clays, contain sufficient sulfur and calcium carbonate 
so that with the oxidation processes which accompany 
drainage, the soil solution is kept saturated with gyp- 
sum for several years. This is a most fortunate cir- 
cumstance because the removal of exchangeable sod i um 
takes place simultaneously with the reduction of salin- 
ity, without the need for the addition of chemical 
amendments. Zuur (1952) has given the data in table 
7 as being typical of changes in the exchangeable- 
cation status of a polder soil following drainage. 

Table 7. -Exchangeable cations in the tops oil of a 
polder reclaimed from salt water (Zuur, 1952) 



Time 


Ca 


Mg 


K 


Na 


Just after drainage 

4 years after ditching 

Final situation 


Per- 
cent 
17 
73 
82 
87 


Per- 
cent 
35 
17 
10 
8 


Per- 
cent 
9 
5 

// 
4 


Per- 
cent 
39 
5 
2 
1 







The reclamation of soils that have been subjected to 
sea-water inundation is an agricultural problem that 
has assumed considerable economic importance and 
has been given a great deal of attention by soil and 
plant scientists. This is particularly serious when it 
occurs on older cultivated soils in humid regions, be- 
cause of the lack of soluble calcium for replacing ex- 
changeable sodium concurrently with the leaching out 
of the soluble salts. Leaching by rain water changes 
the soil from the saline-alkali to the nonsaline-alkali 
condition, with the attendant deterioration of structure. 
Reclamation then requires soluble calcium for replac- 
ing exchangeable sodium and careful management and 
cultural practices for some time to reestablish a favor- 
able physical status of the soil. Van den Berg (1952) 
provides an introduction to the literature on this 
subject. 



Chapter 4 



Plant Response and Crop Selection 
for Saline and Alkali Soils 



Significance of Indicator Plants for 

Saline Soils 

Hilgard (1906) was among the first to recognize the 
significance of certain native plants as indicators of the 
characteristics of soils, and to make use of them in 
determining the availability of saline and alkali soils 
to agriculture. More recently, Sampson (1939, p. 200) 
has stated : 

In the future a broader use of indicator com- 
munities and species is likely, but such use is sure 
to be backed by sounder evidences than it has at 
this time. Preceding this possible broadened use 
there must first be more critical study of the 
growth requirements of both the indicator plant 
and the economic species; only then will the indi- 
cator concept reach its maximum reliance. 

Some progress has been made in developing quan- 
titative methods for the study of the indicator plant 
concept; and, in some areas, data have been obtained 
that relate the growth performance of indicator plants 
and their ability to survive to the physical and chemi- 
cal measurements of the soils in which they grow. 
Kearney and associates (1914) made a quantitative 
study of plant communities as indicators of salinity 
and soil moisture in the Tooele Valley, Utah, and de- 
termined the moisture equivalent, wilting coefficient, 
and salt content for six characteristic plant communi- 
ties. For example, they concluded that land charac- 
terized by a sagebrush association is capable of crop 
production with irrigation, and that a greasewood- 
shadscale type of vegetation indicates land that is suit- 
able for crop production under irrigation only after 
the excess salts are removed by leaching. Harris and 
coworkers (1924, p. 922), working in the same valley, 
found "a close parallelism between physiochemical 
properties of tissue fluids of native species on the one 
hand and the characteristics of the soil and the capacity 
of the land for crop production on the other." 

In connection with investigations of grazing in 
western Utah, Stewart, Cottam, and Hutchings (1940) 
investigated the root penetration of several desert 
plants as influenced by soil salinity and the nature of 
the root system of the plant. They found that roots of 
shadscale readily penetrated soil having 1,000 to 10,000 



p. p. m. salt, but those of sagebrush did not. Billings 
(1945) studied the soil characteristics of several plant 
communities in western Nevada, including greasewood 
and greasewood-shadscale associations, and reported 
data on soil type, texture, pH, and electrical conduc- 
tivity of the soil solution. He found rather high 
alkalinity (pH 8.5 to 9.5) throughout the profile in 
the greasewood association, and conductances of 1 : 5 
soilrwater extracts ranging from 1.6 to 8.4 mmhos/cm. 
in the 2- to 50-cm. depths. 

Roberts (1950) has investigated the chemical effects 
of salt-tolerant shrubs on soils in the semiarid regions 
of western United States, and found that such shrubs 
as greasewood and shadscale were responsible for sig- 
nificant changes in some of the chemical characteristics 
of the soil profile. Data from several hundred field pH 
tests and some laboratory analyses showed striking dif- 
ferences among the pH, exchangeable sodium, and 
total salt content of soils under some species of shrubs 
as compared to those under other species and to the 
soils in intervening barren areas. Soils in a mixed 
shadscale-greasewood association in the Antelope 
Springs silty clay loam in southwestern Utah had a 
higher pH value under greasewood than under shad- 
scale, and both values were higher than the pH of 
barren soil. A similar relationship was found with 
respect to EC e and sodium status. 

Fireman and Hayward (1952) made a quantitative 
study of several indicator plants growing in mixed and 
pure associations in the Escalante Desert, Utah, to 
determine the relation of vigor, age, and distribution 
of indicator plants to the physical and chemical char- 
acteristics of the soils of their habitats, and to compare 
soils occupied by the root systems of indicator plants 
and the soils in the adjacent interspaces. The pH val- 
ues of saturated soil pastes and 1: 10 soil: water sus- 
pensions, particularly of the surface soil, generally were 
higher under shadscale and invariably higher under 
greasewood than under sagebrush or in the adjacent 
bare areas. The ESP of the soil was somewhat higher 
under shadscale and very much higher under grease- 
wood than under sagebrush or in the barren areas, and 
the soluble-salt content was appreciably higher under 
shadscale and greasewood than in adjacent bare soil 
or under other shrubs. 

These and other studies by Flowers (1934), Harris 

55 



56 



AGRICULTURE HANDBOOK 60, U. S. DEPT. OF AGRICULTURE 



(1920) , and Shantz and Piemeisal (1924) indicate that 
a vegetational survey can be useful in appraising an 
area if quantitative data are available regarding the 
soils and the ecology and physiology of the indicator 
plants. However, certain precautions should be taken 
in the use of indicator plants as a basis for the diag- 
nosis of saline and alkali soils. In the first place, it 
would be unwise to appraise land on the basis of a 
single species unless it is a reliable indicator. Some 
species of plants growing in semiarid regions are poor 
indicators, even though they may tolerate large quan- 
tities of salt, because they will also grow very well 
in the absence of salinity or alkali. Tussockgrass, salt- 
grass, and shadscale, especially, tolerate an appreciable 
degree of salinity but will grow well in the absence of 
salt. Even greasewood is not an infallible indicator, 
since it has been found making thrifty growth on 
nonsaline sand dunes. 

A second point to emphasize is the need for very care- 
ful sampling. The studies by Roberts and by Fireman 
and Hayward, cited above, indicate that large differ- 
ences may occur in soil samples from sites only a few 
feet apart, especially when the plant association is a 
mixed one. If a vegetational survey and related soil 
sampling are to serve as a basis for determining the 
suitability of soils for irrigated agriculture, the analysis 
of the plant population and the collection of soil sam- 
ples must take into account the possible effects of the 
indicator plants on the chemical and physical char- 
acteristics of the soil. 

A third consideration relates to the purity and 
density of stand and the vegetative vigor of the various 
species present in the area to be evaluated. In the fol- 
lowing paragraphs, the statements regarding the sig- 
nificance of various indicator plants are based on the 
assumption that they occur in a relatively pure stand 
and that they are growing in a normal manner. In the 
case of mixed associations, the appraisal should take 
into account the indications of all of the dominant 
species in the plant community. 

Several species of plants native to western United 
States are regarded as good indicator plants if the pre- 
cautions noted above are observed. Some of the best 
known indicator plants are listed below, and pertinent 
available data are given regarding their ranges, char- 
acteristics of the soils on which they grow (texture, 
soil moisture, salinity, etc. ) , and the conditions which 
they may indicate with respect to reclamation or soil- 
management practices needed for irrigation agricul- 
ture. The order in which the indicator plants are listed 
is based on the approximate level of soil salinity asso- 
ciated with the occurrence of the species in pure stand 
or as one of the dominant species. The information 
given was compiled from the data and field observa- 
tions of the authors cited in this chapter. 

Indicator Plants 10 

Mesquite (Prosopis juliflora) . — Range: Southern 
Kansas to southeastern California, Baja California and 
Sonora, Mexico, to eastern Texas. Occurs on a variety 



of textural soil classes that are very permeable and 
well-drained, with a low water table and an intermedi- 
ate moisture-holding capacity (SP 25 to 50) , n The 
soils are usually nonsaline throughout the 4-foot profile, 
but salt may accumulate at the surface under some con- 
ditions. Indications : Suitable for agriculture if water 
is available. 

Creosotebush (Larrea tridentata) . — Range: South- 
ern Colorado and southern Utah to west Texas, west to 
California and Mexico. On dry plains and slopes. 
Occurs on soils of coarse and moderately coarse texture 
that are very permeable and well -drained, with low 
water table and low to intermediate moisture-holding 
capacity (SP 15 to 40) . The soils are nonsaline to a 
depth of 4 feet (<0.03 percent) 12 and nonalkali. In- 
dications: Where stands are good, the soils are non- 
saline and of sufficient depth to support a specialized 
agriculture provided water is available. If stands are 
poor, the soils may be shallow, underlain with layers 
of rock or hardpan, and unsuitable for crop production. 

Sagebrush (Artemisia tridentata), — Range: South 
Dakota to British Columbia, south to northern New 
Mexico and northern Arizona; rare in southern Cali- 
fornia. Occurs on loamy soils (loamy sand, gravelly 
loam, sandy loam, loams, silt loam, and clay loam) 
that are more or less permeable and well-drained, and 
the soil moisture may vary from low to high (SP 
15 to 70). The soils are nonsaline (<0.05 percent) 
and nonalkali in the zone occupied by the roots. Indi- 
cations: The soils are suited for irrigation agriculture 
or dryland farming, provided they are in an area where 
precipitation is adequate and the growing season is 
favorable. No reclamation practices are required. 
Sagebrush is not a good indicator of soil texture, be- 
cause it occurs on a wide range of textural classes. It 
may grow well on soils that are too stony for farming. 

Winterfat, or whitesage (Eurotia lanata) . — 
Range: Saskatchewan, Canada, to Washington, south 
to Texas, Arizona, and California. May be in pure 
stands, but frequently occurs in mixed associations 
with shadscale, rabbitbrush, and greasewood. Occurs 
on loamy soils that are permeable and well-drained, 
with a low water table and low to intermediate mois- 
ture-holding capacity (SP 20 to 45). Soils usually 
nonsaline in the first foot or two ( <0.03 percent) , but 
roots may penetrate soil layers having salt in excess 
of 1,000 p. p. m. (0.1 to 0.6 percent). Indications: 
Where winterfat is dominant, the soils are usually non- 
saline, but this plant can tolerate some salt; therefore, 
leaching may be required. 

Desert saltbush (Atriplex polycarpa). — Range: 
Arizona, Nevada, Utah, central California to north- 
western Mexico. Occurs on moderately coarse-textured 
soils (sandy loam, fine sandy loam) that are moist in 
winter and dry in summer and fall. The water table 



10 The authors acknowledge the assistance of W. G. Harper, 
Division of Soil Survey, in the preparation of this section. 



ii 



See Method 3b for estimating saturation percentage (SP) 
in coarse-textured soils. 

12 Values for salinity in this and following statements are 
given as percent salt (dry-weight basis). 



SALINE AND ALKALI SOILS 



57 



is usually low, and the moisture-holding capacity is 
intermediate (SP 25 to 50) . The soils may be non- 
saline in the first foot, but they usually contain some 
salt in the subsoil (0.04 to 0.5 percent). Indications: 
Where stands are pure and growth is good, the soils 
are nonsaline or slightly saline and are suitable for 
irrigation agriculture. Where growth is poor, there 
may be a limy hardpan or salt in the subsoil. Leach- 
ing and drainage may be necessary. 

Arrowweed (Pluchea sericea). — Range: Texas, 
southern Utah, southern California, and northern 
Mexico. Occurs on loamy soils which are usually 
permeable, with an intermediate moisture-holding 
capacity (SP 30 to 50) . There is usually a high water 
table or available moisture below the first foot 
throughout the year. It frequently occurs with the 
saltbush (Atriplex lentiformis) , but it is less salt toler- 
ant than that plant. The soils may be strongly saline 
in the surface foot (0.6 to 2.0 percent), the salinity 
decreasing with depth (0.1 to 0.5 percent in the fourth 
foot). Indications: The soils are usually saline or 
strongly saline; but, where the subsoil is permeable, the 
land is suitable for agriculture after drainage and 
leaching. 

Shadscale (Atriplex con j erti folia) . — Range: North 
Dakota to Oregon, south to New Mexico, northern 
Arizona, and California. Plains and valleys in moun- 
tainous areas. Usually occurs on medium to mod- 
erately fine-textured soils. The soils have an inter- 
mediate to high moisture-holding capacity (SP 25 to 
60), may have restricted permeability, and a high 
water table may develop, depending upon subsoil con- 
ditions. The soils are nonsaline to slightly saline in 
the first foot (0.02 to 0.1 percent) , the salinity increas- 
ing with depth (0.3 to 1.0 percent). The soils may 
contain exchangeable sodium, and the pH of the sur- 
face soil may exceed a value of 9.0. Indications: Shad- 
scale is salt and alkali tolerant, but it has a wide range 
of tolerance and may grow well on soils that are non- 
saline or slightly saline. It usually indicates a soil 
with harmful amounts of salt or exchangeable sodium 
in the subsoil. The soils may be farmed after leaching, 
but drainage may be required. 

Greenmolly (Kochia americana) . — Range: Wyo- 
ming to northeastern California, south to northern 
Arizona and New Mexico. Occurs on medium- to fine- 
textured soils that are usually homogeneous to a depth 
of several feet. They may puddle easily, and the per- 
meability is lower than that on sagebrush lands, which 
frequently adjoin Kochia associations. Soil moisture 
is intermediate to high (SP 40 to 70), and there may 
be a high water table. The salinity is moderately low 
in the first foot (0.12 to 0.3 percent), but it increases 
with depth so that the second to fourth feet may be 
strongly saline (0.55 to 1.5 percent) . Since Kochia 
tends to have a shallow root system which does not 
penetrate the more saline deeper portions of the pro- 
file, it should not be regarded as especially salt tolerant. 
Indications: Pure stands of Kochia occur in soils that 
are low in salt in the first foot but have a saline subsoil. 



Leaching and drainage are required, and suitability of 
such land for irrigation agriculture is doubtful. 

Alkali- heath (Frankenia grandifolia var. cam- 
pestris) . — Range: Central and southern California and 
Nevada. On low-lying lands and alkali flats. Occurs 
on soils of various textures (sandy loams to fine-tex- 
tured loams) with soil-moisture conditions which vary 
from well -drained to wet with a high water table. The 
salinity is also variable, ranging from low to very high 
(0.02 to 2.0 percent) , and exchangeable sodium is fre- 
quently present. Indications: Where alkali-heath is 
growing luxuriantly in a uniform stand, the soils are 
generally highly saline and the lands are unsuitable 
for agriculture unless they are drained and leached. 
Where growth is sparse, the soil may be much less saline 
and easier to reclaim. 

Greasewood (Sarcobatus vermiculatus) . — Range: 
North Dakota to Alberta, Canada, south to California, 
Arizona, and northern Mexico; rare in California and 
southern Arizona. Usually occurs on fine-textured 
soils (clay, clay loam) but occasionally on soils of 
coarser texture. The moisture content of the soil is 
intermediate to high (SP 45 to 70), especially below 
the second foot, permeability may be restricted, and 
frequently the water table is high. The soils are gen- 
erally saline- alkali; the range of salinity is wide (0.05 
to 1.6 percent) and varies with depth; exchangeable 
sodium is present in most areas and the values are 
moderate to high. Indications: Greasewood is very 
salt and alkali tolerant, and usually indicates a fine- 
textured, relatively impervious soil with high salinity 
and exchangeable sodium. Drainage and leaching are 
required, and amendments may be necessary. 

Cressa (Cressa truxillensis) . — Range: Texas to 
southern Utah and southern California and Mexico. 
Occurs on saline flats where the soils are fine-textured, 
usually moist, with restricted permeability. The 
salinity is very high (1.0 to 2.0 percent) . Indications: 
Cressa is a good indicator of saline soil and is more 
reliable than alkali-heath, because the range of salinity 
under which it grows is less variable. The soils require 
drainage and leaching. 

Saltgrass (Distichlis stricta). — Range: Saskatche- 
wan to Washington, south to Texas, Arizona, and 
California. On salt flats and wet meadows. Occurs on 
soils of various textures, but it is most commonly found 
on loamy soils. The moisture-holding capacity is 
usually high (SP 45 to 90), and the soils are moist or 
wet throughout much of the year with a high water 
table. The salt content of the 4-foot profile is usually 
high (0.8 to 2.0 percent), with the highest content in 
the first foot. However, good stands may occur on soils 
containing very small amounts of salt (0.05 percent). 
Exchangeable sodium may or may not be present. In- 
dications: Usually indicates wet, strongly saline soils 
with high water tables, but the plant may occur in 
areas low in salinity. Drainage and leaching are 
essential. 

Saltwort, or seepweed (Suaeda spp.). — Range: 
Alberta to Oregon, south to northern Mexico. Salt 
flats and marshes. Occurs on loamy soils of varying 



259525 O - 54 - 5 



58 



AGRICULTURE HANDBOOK 60, U. S. DEPT. OF AGRICULTURE 



textures which may be puddled and underlain with 
hardpan. Usually found on moist seep lands with 
high water tables but may occur on better drained land. 
Moisture-holding capacity is intermediate to high 
(SP 30 to 60) . The soils are saline or saline-alkali, 
with high concentrations of salt in the first foot (0.6 
to 3.2 percent) and decreasing amounts with depth, 
but the average salinity for a 4-foot profile may exceed 
1 percent where the growth is luxuriant. The soils may 
contain exchangeable sodium. Indications: Where 
virgin growth is vigorous, seepweed is a good indicator 
of highly saline or saline-alkali soil. Drainage and 
leaching are essential, and amendments may be 
required. 

Alkali sacaton, or tussockgrass (Sporobolus 
airoides) . — Range: South Dakota to Washington, 
south to Texas, Arizona, and southern California. In 
low, wet areas, and river valleys. Occurs on loamy 
and clayey soils that have an intermediate to high 
moisture-holding capacity (SP 45 to 75) . The soil sur- 
face is moist a great part of the year, and the water 
table is usually high. The salinity of the soil may vary 
within wide limits (0.3 to >3.0 percent), the higher 
values being in the first foot; but the plant grows best 
in the lower range (0.3 to 0.5 percent). Exchangeable 
sodium may be present, and this grass is very tolerant 
to it. Indications : In pure, vigorous stands, this plant 
is a good indicator of wet, very saline or saline-alkali 
soils, with a high water table. It may occur on soils 
without a high moisture content in the subsoil on sites 
receiving runoff water. The land requires drainage 
and leaching, and soil amendments may be needed 
unless gypsum is present. 

Samphire, or glasswort (Salicornia spp.).— 
Range: Saskatchewan to British Columbia, south 
through Colorado and Nevada. On salt flats and along 
shores of saline ponds and lakes. Occurs on fine- 
textured clayey soils that are very wet throughout the 
profile, with high water tables. The salinity is very 
high, and this plant grows well where salt may average 
1 to 4 percent in the 4-foot profile. Exchangeable 
sodium may be present in varying amounts. Indica- 
tions: Soils are usually very wet, with excessive 
salinity. Useless for agriculture without drainage and 
prolonged leaching. 

Pickleweed, or iodinebush (Allenrolfea occiden- 
talis). — Range: Oregon to Baja California, Mexico, 
east through Arizona and New Mexico to western Texas. 
On saline flats. Occurs on a wide range of soil textures 
(loamy and clayey soils), but usually on fine-textured 
soils. The soils are moist or wet throughout the year, 
with high water tables that may be close to the surface.* 
The soils are excessively saline in the first foot (1.0 to 
>2.5 percent) and are very saline throughout the 4-foot 
profile (average 1.0 to 1.5 percent), but the salinity 
decreases somewhat with depth. Exchangeable sodium 
may be present in varying amounts. Indications: Soils 
are usually fine-textured, very wet, and excessively 
saline. If the stand is good, the land is not suited for 
agriculture without drainage and prolonged leaching. 



Crop Response on Saline Soils 

A field of crop plants growing on saline soil usually 
has barren spots, stunted growth of the plants with con- 
siderable variability in size, and a deep blue-green 
foliage; but these features are not invariable indica- 
tions of salinity. For example, barren spots may occur 
in nonsaline fields because of faulty leveling and the 
resultant inadequacy of irrigation ; and retarded growth 
and abnormal color may result from nutrient 
deficiencies. 

The extent and frequency of bare spots in many areas 
may be taken as an index of the concentration of salt 
in the soil. Inasmuch as most plants are more sensitive 
to salinity during germination than in later stages of 
growth, barren spots are more indicative of salinity 
around the seed during germination than they are of 
the general salinity status of the soil profile. Fre- 
quently, cultural practices contribute to an accumula- 
tion of salt around the germinating seed with resultant 
failure in germination. The vigor of the plants adja- 
cent to barren spots may indicate the distribution of 
salt in the soil. Full-sized vigorous plants immediately 
adjacent to a bare spot suggest a local concentration of 
salt, while stunted plants in this position indicate a more 
general distribution of salinity in the area. If the 
level of salinity is not sufficiently high to result in 
barren spots, the major characteristic in the appearance 
of the crop may be a marked irregularity in vegetative 
vigor. 

Caution should be exercised to avoid confusion be- 
tween effects of low soil fertility and those caused by 
salinity. Plants that are stunted because of low fer- 
tility are usually yellowish green, whereas those stunted 
owing to salinity are characteristically blue green. The 
bluish appearance is the result of an unusually heavy 
waxy coating on the surface of the leaves, and the 
darker color to an increase in the chlorophyll content 
on a surface-area or fresh-weight basis. Sugar beets, 
crucifers (cabbage, mustards, and related species), 
alfalfa, some clovers, grasses, and other crops generally 
develop a noticeable blue-green coloration when grown 
on saline soils. 

There are many regions where plants may develop 
an intense chlorosis because of certain soil conditions. 
The causes of chlorosis are not fully understood, but 
this condition is frequently associated with calcareous 
soils or, in some cases, with the use of irrigation waters 
of high bicarbonate content (Harley and Lindner, 
1945). Although calcium carbonate is relatively in- 
soluble, much crop injury is associated with its pres- 
ence. Since this soil condition frequently occurs in 
the absence of an accumulation of soluble salts, chloro- 
sis cannot be regarded as a definite symptom of salinity. 

Some species of plants develop characteristic necrotic 
areas, tipburn, and firing of the margins of the leaves 
when grown on saline soil. Many stone fruits, avo- 
cado, grapefruit, and some of the less salt-tolerant 
varieties of cotton belong in this category. 

The cupping or rolling of leaves is a common mani- 
festation of moisture deficiency in plants, but these 



SALINE AND ALKALI SOILS 



59 



symptoms may be indicative of salinity when they 
occur in the presence of apparently adequate soil mois- 
ture; however, other factors that cause malfunction of 
the root system, such as root diseases and high water 
tables, may produce similar leaf symptoms. While the 
appearance of the crop may, therefore, be indicative of 
saline conditions, a reliable diagnosis of salinity usually 
requires additional evidence derived from appropriate 
soil and plant tests. 

Salinity and Water Availability 

Numerous laboratory experiments with sand and 
water cultures have demonstrated the close relationship 
between plant growth and the osmotic pressure of the 
culture solution. On a weight or equivalent basis, 
chloride salts are generally more inhibitory to the 
growth of plants than sulfate salts, but this difference 
tends to disappear when concentrations are expressed 
on an osmotic basis. These relationships indicate that 
it is the total concentration of solute particles in the 
solution rather than their chemical nature which is 
mainly responsible for the inhibitory effects of saline 



solutions on the growth of crop plants. Direct experi- 
mental evidence of the influence of osmotic concentra- 
tion on water uptake by plant roots has been reported 
by Hayward and Spurr (1944). In addition to the 
osmotic pressure of the solution, the nature of the 
salts present may exert an important influence on plant 
growth. Such specific ion effects are discussed in a 
subsequent section. 

There is much evidence to indicate that an increase 
in the osmotic pressure of the soil solution may result 
in a decrease in the water uptake by plant roots, but 
an additional factor must be taken into account in 
dealing with the soil system; that is, soil-moisture ten- 
sion, or the molecular attraction of the surface of the 
soil particles for water. Soil-moisture tension increases 
as the soil becomes drier and the water films around 
the soil particles become thinner. This equivalent 
negative pressure is apparently additive to the osmotic 
pressure of the soil solution in limiting the availability 
of water to plant roots. The sum of soil-moisture ten- 
sion and the osmotic pressure of the soil solution is 
termed "total soil -moisture stress." Studies on the 
effects on growth of several moisture treatments and 



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INTEGRATED MOISTURE STRESS 
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Figure 17. — Growth of bean plants as influenced by total soil-moislure stress. The salinity level for each treatment is indicated as 

percentage on a dry-soil basis (Wadleigh and Ayers, 1945). 



60 



AGRICULTURE HANDBOOK 60, U. S. DEPT. OF AGRICULTURE 



salinity levels indicate that plant growth is a function 
of total soil-moisture stress, regardless of whether this 
stress arises primarily from salinity or moisture tension 

(% 17)- , , , 

It is possible to extract the soil solution and deter- 
mine its osmotic pressure, but this procedure is seldom 
used because it is simpler to estimate salt concentra- 
tion by determining the electrical conductivity of the 
saturation extract (EC e ) . Since saturation percentage 
is related to the field-moisture range, EC e bears a close 
relationship to the EC of the soil solution. The rela- 
tionship between EC and the osmotic pressure of satura- 
tion extracts is given in figure 6. The EC e , therefore, 
provides information on the concentration of salt in 
the soil solution and its osmotic properties. The yield 
of orchardgrass when grown on soil to which various 



single salts had been added indicated that growth was 
simply related to salinity, expressed in terms of EC e 
for various neutral salts (fig. 18). The response to 
sodium bicarbonate was, however, exceptional. In this 
case, calcium and magnesium ions from the soil 
exchange complex were precipitated as carbonates, 
thereby greatly increasing the exchangeable-sodium- 
percentage and producing an alkali soil. 

The Scofield scale, in which crop response to 
salinity under average conditions is expressed in terms 
of the conductivity of the saturation extract, was dis- 
cussed in chapter 2. This salinity scale has been widely 
used for a number of years and has been found to be 
satisfactory for salinity appraisal. To facilitate the 
discussion of plant response on saline soils, this salinity 
scale in its latest modified form is given again. 



Salinity effects mostly 
negligible 



Yields of very sensitive 
crops may be restricted 



Yields of many crops 
restricted 



Only tolerant crops 
yield satisfactorily 



Only a few very tolerant 
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CONDUCTIVITY OF THE SATURATION EXTRACT 



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Figure 18.— Growth of orchardgrass, as influenced by various salts added to a sandy loam soil (Wadleigh and others, 1951) . 



SALINE AND ALKALI SOILS 



61 



It should be emphasized that this classification of 
plant growth in relation to various salinity levels refers 
to the salt status of the soil in the active root zone. It 
is possible to obtain samples from the surface soil 
around the base of row crops that may contain 5 per- 
cent salt or more with EC e values of 50 mmhos/cm. or 
higher. This high concentration of salt represents an 
accumulation in the bed during the growth of the plants 
and not the salt concentration in the active root zone. 
Therefore, in correlating crop growth with salinity, 
care should be exercised to take soil samples from the 
active root zone that are uncontaminated by surface in- 
crustations of salt. With row crops, the mass of soil 
making up the bed is frequently more saline than the 
soil below the furrow, and studies of root distribution 
and water uptake by plants indicate that under such 
conditions the major root activity occurs in the less 
saline parts of the soil, as shown in figure 14. These 
considerations should be borne in mind in determining 
the salt status of a soil with reference to plant response. 

A technique for measuring the freezing point of soil 
moisture has been developed that provides a rapid, use- 
ful method for obtaining, by a single determination, 
the total moisture stress in a soil sample at field- 
moisture conditions (Method 6b). This eliminates 
errors caused by dilution of the soil solution and the 
resultant dissolving of moderately soluble salts, such 
as gypsum. Total soil-moisture-stress values obtained 
by freezing-point measurements are in good agreement 
with previously used methods involving determination 
of EC e and moisture tension for the soil studied ( Wad- 
leigh, 1946, and Ayers and Campbell, 1951). 

The experimental evidence cited above supports the 
concept that decreased growth on saline substrates is 
related to decreased water availability, but certain re- 
lationships between plant and substrate are still not 
fully understood. Despite marked decreases in growth 
with increasing concentration of the substrate, osmotic 
gradients between tops of plants and substrate are 
sometimes unaffected by increased osmotic pressure or 
total soil-moisture stress of the substrate. This is 
caused by increases in osmotic pressure of aerial parts 
of the plant that parallel increases in osmotic pressure 
of the substrate (Eaton, 1942). In addition, the 
osmotic pressure of expressed tissue fluids from the 
tops of plants does not appear to be correlated with 
the salt tolerance of some species. It is possible, how- 
ever, that such measurements of osmotic gradient be- 
tween plant tops and substrate may not represent the 
effective osmotic force which limits water absorption by 
the roots. 

Specific Ion Effects 

The previous discussion has dealt primarily with 
the effect of soluble salts in limiting the availability 
of moisture to plants. Other effects of salt may be 
equally important in restricting the growth of certain 
species. Injury or growth depression of plants, which 
cannot be accounted for on the basis of the osmotic 
pressure of the solution, will be referred to as a toxic 
effect of the salt in question. It should be recognized 



that toxicity so defined need not involve a direct effect 
of the salt or ions, either on surface membranes of plant 
roots or in the plant tissues. Frequently, toxicity may 
be caused, in part, at least, through effects on the uptake 
or metabolism of essential nutrients. As it is not always 
possible to distinguish clearly the mechanism under- 
lying specific ion effects, it is convenient to refer to such 
phenomena as toxicities in contrast to the general os- 
motic effect of salt on plant growth. 

The influence of excessive concentrations of specific 
salts on plant growth is an extremely complex subject 
involving many fundamental principles of plant nutri- 
tion. It is beyond the scope of this handbook to review 
the voluminous and diversified literature bearing on 
this subject. Much of the pertinent literature is cited 
in a review by Hay ward and Wadleigh ( 1949) . Litera- 
ture citations in the following discussion are restricted 
mainly to papers of special significance in connection 
with certain topics not considered in the review cited 
above. 

Ions that are frequently found in excess in saline 
soils include chloride, sulfate, bicarbonate, sodium, 
calcium, and magnesium. Less frequently encountered 
in excessive amounts are potassium and nitrate. The 
effects of all these ions on plant growth are being inves- 
tigated by comparing plant response to isosmotic solu- 
tions of different salts. Species and even varietal dif- 
ferences among plants make it difficult to generalize 
regarding the toxicity of various salts or ions. It ap- 
pears, however, that differences in plant tolerance to 
excessive concentrations of ions in the substrate are 
related, in some degree, to specific selectivity in ion 
absorption and nutrient requirements of the plants. In 
addition to these factors, there is also a marked dif- 
ference among species in the amounts of such ions as 
sodium and chloride that can be accumulated without 
toxic effects. 

Before considering specific toxic effects caused by 
excessive concentrations of soluble salts, other effects 
of certain ions deserve some mention. Although not 
considered essential plant nutrients, sodium and chlo- 
ride, when present in relatively small concentrations, 
may stimulate the productivity of certain crops. Thus, 
Harmer and Benne (1941) have attributed increased 
yields of beets, celery, Swiss chard, and turnips to 
sodium. These authors consider sodium to be "nearly 
as much needed as a nutrient for these crops as is the 
potassium ion." Other investigators believe the effect 
of sodium to be more indirect, either substituting to 
some degree where potassium is deficient (Lehr, 1949; 
Dorph-Petersen and Steenbjerg, 1950) or limiting ex- 
cessive accumulation of calcium, which with beets 
results in the development of a "calcium-type plant" 
characterized by a blue-green color and stunted growth 
(Lehr, 1942) . Chloride, like sodium, has been ob- 
served to increase yields of some crops, notably beets, 
spinach, and tomato (Hay ward and Wadleigh, 1949). 
On the other hand, chloride salts have long been known 
to affect adversely the quality of such crops as potatoes 
and tobacco. However, on saline soils, chloride and 
sodium ions occur in much higher concentrations than 



62 



AGRICULTURE HANDBOOK 60, U. S. DEPT. OF AGRICULTURE 



customarily employed in fertilizer studies. Under such 
conditions the high osmotic pressure of the soil solu- 
tion tends to obscure specific effects of sodium or chlo- 
ride on crop yields and quality (Bernstein and others, 
1951). 

Sodium 

Plant species vary greatly in the amounts of sodium 
that they may accumulate, and many species tend to 
exclude sodium from their leaves, although they may 
accumulate it in their stems or roots. Notwithstand- 
ing this extreme selectivity in accumulation of sodium 
by plants, few well-defined instances of sodium toxicity 
have been reported. Lilleland and coworkers (1945) 
described a tipburn of almond leaves that is related 
to sodium content, and Ayers and associates (1951) 
have described a sodium-scorch of avocado leaves. In 
both studies, the soils on which affected trees grew were 
sufficiently low in soluble salts and exchangeable sodi- 
um to be regarded as nonsaline and nonalkali. 
Although sodium salts in water cultures rarely cause 
toxic plant reactions, stone-fruit trees (Brown and 
others, 1953) and avocados (Ayers, 1950) evidenced 
the same types of leaf injury in sand or water cultures 
containing added sodium salts as were observed in the 
field, thus confirming the relationship of sodium to 
leaf injury in these species. Unpublished data by 
Wadleigh and Gauch indicate that leaf burn in salt- 
sensitive cotton varieties is closely correlated with the 
sodium content of leaves. 

Sodium in the soil may exert important secondary 
effects on plant growth through adverse structural modi- 
fications of the soil. Thus, if the exchange complex con- 
tains appreciable amounts of sodium, the soil may be- 
come dispersed and puddled, thereby causing poor 
aeration and low water availability (McGeorge and 
Breazeale, 1938) . This is especially true in fine-textured 
soils. Also, if the exchange complex becomes more 
than 40 to 50 percent saturated with sodium, nutri- 
tional disturbances may result (Ratner, 1935; Thorne, 
1945). Ratner (1944) stated that under such condi- 
tions the exchange complex actually removes calcium 
from the root tissues of the plant and that death may 
ensue because of calcium deficiency. Laboratory ex- 
periments have shown that the addition of calcium, and 
sometimes magnesium, to alkali soils can improve plant 
growth very markedly with an associated increase in 
the uptake of these added elements by the plants (Bower 
and Turk, 1946) . 

Bower and Wadleigh (1949), using amberlite resins, 
determined the effects of various levels of exchangeable 
sodium on cationic accumulation and growth of four 
species of plants. The effect of increasing levels of ex- 
changeable sodium on cationic accumulation varied 
among the species and between tops and roots of a given 
species and was related to inherent specificity of the 
species in accumulating the several cations. In general, 
increasing the exchangeable-sodium-percentage of the 
substrate resulted in a decreased accumulation of cal- 
cium, magnesium, and potassium in the plants. 



Calcium 

The effect of high concentrations of calcium ions in 
saline soil solutions varies with the species. Some 
species, such as guayule, are more tolerant of added 
calcium salts than of other neutral salts (Wadleigh and 
Gauch, 1944). Masaewa (1936), however, found 
added calcium chloride to be more toxic to soil cul- 
tures of flax than added sodium chloride. Wadleigh 
and coworkers (1951) have reported specific toxicity 
of calcium salts added to soil cultures of orchardgrass, 
and unpublished data by Ayers indicate a similar rela- 
tion for tall fescue. Both the calcium and chloride 
contents of the grasses from the calcium chloride treat- 
ments increased markedly; but since calcium nitrate 
produced a toxic effect similar to that of calcium 
chloride, the toxicity was attributed to calcium accumu- 
lation rather than to chloride (Wadleigh and coworkers, 
1951). Moderate concentrations of calcium chloride 
are highly toxic to stone fruits in sand culture, and it 
appears that this toxicity is associated with an accumu- 
lation of chloride in the leaves. This chloride accumu- 
lation is more pronounced in the presence of excess 
calcium ions than when sodium occurs in excess (Brown 
and others, 1953) . 

Magnesium 

High concentrations of magnesium in the substrate 
are frequently more toxic to plants than isosmotic con- 
centrations of other neutral salts. This toxicity of 
magnesium may be alleviated by the presence of rela- 
tively high concentrations of calcium ions in the 
substrate. 

Potassium 

Although the occurrence of high concentrations of 
potassium in the soil solution is rare, toxic effects of 
high potassium have been reported. There is evidence 
to indicate that toxicity of high potassium, like that of 
high magnesium, may be lessened when balanced by 
high calcium concentrations. High concentrations of 
potassium may also induce magnesium deficiency 
(Boynton and Burrell, 1944) and iron chlorosis 
(Walsh and Clarke, 1942). 

Chloride 

As indicated under the discussion of calcium toxicity, 
the accumulation of chloride ion in plant tissues mani- 
festing toxic symptoms is not an infallible indication 
of the specific toxicity of chloride. Many plant species 
are no more sensitive to chloride salts than they are to 
isosmotic concentrations of sulfate salts. There is good 
evidence, however, for the specific toxicity of chloride 
to some tree and vine crops. Hay ward and associates 
(1946) and Brown and coworkers (1953) have found 
chloride salts to be toxic to peaches and other stone 
fruits, and Harper (1946) has reported chloride burn 
of pecan and native tree species of Oklahoma. Chloride 
burn has also been reported for citrus (Reed and Haas, 
1924; Cooper and Gorton, 1951), avocados (Ayers, 



SALINE AND ALKALI SOILS 



63 



1950; Ayers and others, 1951; Cooper, 1951), and 
grapevines (Thomas, 1934; Ravikovitch and Bidner, 
1937). 

Reference has been made in the discussion on toxic 
effects of high concentrations of potassium and magne- 
sium to the ameliorative effects of increased concentra- 
tions of calcium. In such cases, high concentrations of 
potassium or magnesium result in increased absorption 
of these ions and decreased absorption of calcium; 
hence, the beneficial effect of increasing the calcium 
concentration in the substrate. It is pertinent, at this 
point, to consider whether such effects occur in the 
anion nutrition of plants; specifically, whether high 
levels of chloride (or sulfate) may interfere with nitro- 
gen, phosphorus, or sulfur nutrition. Available evi- 
dence indicates that such interference in absorption of 
essential anions from saline substrates is of relatively 
minor importance and that decreased growth on saline 
media is not related in any appreciable degree to de- 
creased availability of essential anions. However, 
Breazeale and McGeorge (1932) have emphasized the 
importance of decreased availability of phosphorus and 
nitrogen in calcareous alkali soils. 

Sulfate 

Specific sensitivity of plants to high sulfate concen- 
trations has been noted for a number of crops, and it 
appears that such sensitivity is related to the tendency of 
high sulfate concentrations to limit the uptake of cal- 
cium by plants. Associated with this decrease in cal- 
cium are increases in the absorption of sodium and 
potassium, so that harmful effects of high sulfate in the 
substrate may be related to a disturbance of optimum 
cationic balance within the plant. 

Bicarbonate 

Plant species differ markedly in their tolerance to the 
bicarbonate ion, which sometimes exerts specific toxic 
effects, resulting in serious injury even at low osmotic 
concentrations. Beans and Dallis grass are very sensi- 
tive, while Rhodes grass and beets are relatively tolerant 
(Wadleigh and Brown, 1952; Gauch and Wadleigh, 
1951) . Studies in sand culture indicate that the bicar- 
bonate ion affects the uptake and metabolism of nu- 
trients by plants and that the nature of these effects 
varies with the plant species. For example, bean plants 
in the presence of the bicarbonate ion contain less 
calcium and more potassium than control plants, while 
the main effects in beets are a decrease in magnesium 
and an increase in sodium content. The pattern of 
effects is obviously related to the inherent selectivity 
of species in relation to mineral nutrition. 

The studies by Wadleigh and coworkers cited above 
are of interest in connection with the problem of lime- 
induced chlorosis. Chlorotic symptoms and associated 
divergences in metabolism, involving contents of active 
iron, organic acid fractions, and essential cations, 
are very similar for typical cases of lime-induced chlo- 
rosis (Iljin, 1951, 1952; McGeorge, 1949) and bicar- 
bonate-induced chlorosis. Since the basic causes of 



these chloroses are not understood, it would be specu- 
lative to suggest any closer relationship of the two dis- 
orders than the common features indicate. Thorne 
and others (1951) have shown that chloroses owing to 
such diverse causes as development in darkness, zinc 
deficiency, virus infection, and lime-induced chlorosis 
may be accompanied by very similar changes in potas- 
sium accumulation, water-soluble nitrogen fraction, and 
other features frequently considered characteristic of 
lime-induced chlorosis. 

Boron 

In addition to the elements that frequently occur in 
relatively high concentrations, boron may cause injury 
to plants even when present in very low concentrations 
in the soil solution. Boron is essential to the normal 
growth of all plants, but the concentration required is 
very small and if exceeded may cause injury. Plant 
species vary both in boron requirements and in toler- 
ance to excess boron, so that concentrations necessary 
for the growth of plants having high boron require- 
ments may be toxic for plants sensitive to boron. 

Symptoms of boron injury may include characteristic 
burning, chlorosis, and necrosis, although some boron- 
sensitive species do not develop perceptible symptoms. 
Citrus, avocados, persimmons, and many other species 
develop a tipburn or marginal burn of mature leaves, 
accompanied by chlorosis of interveinal tissue. Boron 
injury to walnut leaves is characterized by marginal 
burn and brown necrotic areas between the veins. Stone- 
fruit trees, apples, and pears are sensitive to boron, but 
they do not accumulate it in high concentration in their 
leaves nor do they develop typical leaf symptoms. Cot- 
ton, grapes, potatoes, beans, peas, and several other 
plants show marginal burning and a cupping of the 
leaf that results from a restriction of the growth of 
the margin. 

Boron toxicity occurs in limited, scattered areas in 
arid or semiarid regions. While its incidence is not 
restricted to saline or alkali soils, excess boron is 
frequently present in saline soils. 

Plant Analysis 

The normal mineral composition of plant parts is 
frequently altered under saline- or alkali-soil condi- 
tions, and analysis of appropriate plant organs may 
serve for diagnosing mineral excesses as well as for 
mineral deficiencies of soils. In addition, plant analysis 
may indicate salt injury in cases where the soil is re- 
garded as nonsaline. This condition may occur with 
plants that are very sensitive to salt, such as beans and 
stone fruits, or in cases where the soil salinity is 
transitory. 

Under some conditions, as in the presence of the 
bicarbonate ion, the entire complex of factors in the 
mineral composition of plants may be altered, and cau- 
tion should be exercised in relating malfunction of 
these plants to a specific ion. Frequently, excessive 
accumulation of an ion in the plant may be the result 
of conditions other than high concentration of that 



64 



AGRICULTURAL HANDBOOK 60, U. S. DEPT. OF AGRICULTURE 



ion in the soil solution. Any factors that inhibit plant 
growth, such as mineral deficiencies and high moisture 
stress, may result in abnormal accumulation of ions in 
plant tissues. For example, plants deficient in potas- 
sium will often show greater accumulation of calcium, 
magnesium, or sodium than normal plants (Cooil, 
1948). Owing to the high degree of variability in the 
composition of "normal" plants under diverse growing 
conditions, the chemical composition of plant parts 
should usually be considered as only one line of evi- 
dence in the diagnosis of crop injury on saline or alkali 
soils. Appropriate soil tests, as described elsewhere in 
this handbook, may be used to furnish corroborative 
evidence. 

Eaton (1942) has pointed out that no particular 
range of salt concentration in the substrate is critical 
in retarding plant growth. Growth depression is usually 
progressive as salt concentration increases. This type 
of relationship is to be expected in cases characterized 
by a predominance of the osmotic factor in limiting 
growth on saline substrates. Correspondingly, there 
is usually a progressive increase in salt concentration in 
the plant tissues as salinity in the substrate increases, 
although frequently the curve relating concentration of 
a specific ion in the leaves to that in the substrate may 
be exponential rather than linear. Considering the 
progressive nature of growth depression and ionic ac- 
cumulation, it becomes apparent that for such cases no 
critical level of salt concentration in the tissues can be 
established with reference to the onset of "salt injury." 
In some instances, however, specific toxic effects of an 
ion may be of predominant importance in limiting 
plant growth. In extreme cases, death may ensue, 
whereas isosrnotic concentrations of salts not spe- 
cifically toxic to the species may cause only minor 
growth depression. Under such conditions, fairly defi- 
nite limits of accumulation of ions, such as sodium or 
chloride, have been observed to be associated with the 
development of toxic symptoms in certain plant species. 

Foliar analysis is commonly used in studying salt 
accumulation. The relationships between foliar com- 
position and the principal ions that occur in excess in 
saline soils can be summarized as follows: (1) Chlo- 
ride concentration in leaves usually bears a close rela- 
tionship to the chloride concentration of the substrate ; 
(2) excessive sulfate in the substrate causes small rela- 
tive increases in total sulfur of the leaf tissue ; ( 3 ) in- 
creases in calcium concentration in leaves are frequently 
associated with excess calcium in the substrate; (4) 
excess soluble sodium may or may not be reflected in 
the sodium content of leaf tissues. The influence of 
high exchangeable-sodium-percentage in depressing the 
calcium concentration of plant tissues has been men- 
tioned in an earlier section. 

Recent studies have furnished information on levels 
of chloride and sodium accumulation in leaf tissues 
associated with leaf injury. Rootstock studies by 
Cooper and Gorton (1951) and Cooper and associates 
(1951 and 1952) indicate that grapefruit and Valencia 
orange may develop leaf burn when chloride accumula- 
tion reaches about 1.0 to 1.5 percent on a dry- weight 



basis, whereas bronzing may occur with even lower 
chloride accumulation. Avocados appear to be more 
sensitive than citrus, since leaf tipburn symptoms were 
reported at chloride concentrations of 0.5 to 0.9 percent 
(Ayers, 1950; Haas, 1950; Aye rs and coworkers, 1951; 
Cooper, 1951). Cooper and Gorton (1951) have ob- 
served tipburn symptoms when chloride was only 0.2 
percent. Burning of peach leaves has been noted when 
chloride content reached 1.0 percent (Hayward and 
others, 1946) ; and, in a study of six varieties of stone 
fruits, leaf burn was not observed until chloride levels 
reached values of 0.6 to 1.8 percent of the dry weight of 
the leaves, depending on the variety (Brown and others, 
1953). Plum and prune showed leaf-burn symptoms 
with about 0.6 percent chloride in the leaves, while 
burning occurred in peach and apricot at 1.0 percent 
chloride. The leaves of the two almond varieties, Non- 
pareil and Texas, developed burn at 1.2 and 1.8 percent, 
respectively. In a study of salt injury to pecans and 
native trees of Oklahoma, Harper (1946) found ap- 
proximately 0.6 percent chloride to be associated with 
the development of leaf-burn symptoms. Thomas 
(1934) observed leaf burn of grapes having a chloride 
content of 0.5 percent, and Ravikovitch and Bidner 
( 1937) found 1.2 percent. The latter reported that the 
variety Chasselas accumulated as much as 3.0 percent 
chloride in severely burned leaves, while the variety 
Muscat Hamburg accumulated a maximum of 1.5 per- 
cent. Such varietal differences in levels of chloride ac- 
cumulation doubtless will be found for other crops. 

Other factors that may affect the level of accumulated 
chloride include age of leaf, season, and climatic con- 
ditions. Brown and coworkers (1953) and Thomas 
(1934) reported increasing levels of chloride in leaves 
of stone fruits and grapes, respectively, as the season 
progressed. Hot, windy weather may result in very 
rapid chloride accumulation in leaves in a very short 
time (Thomas, 1934) ; and, under such conditions, 
higher chloride levels may appear to be critical in the 
development of leaf injury. Although chloride con- 
tents of 0.5 to 1.0 percent may be associated with foliar 
injury of some crops, it should be pointed out that many 
species of plants, including some possessing no out- 
standing salt tolerance, such as potatoes, may accumu- 
late as much as 5.0 percent chloride on a dry-weight 
basis without showing foliar symptoms (Bernstein and 
associates, 1951 ) . 

While the causal relationship between chloride ac- 
cumulation and leaf symptoms has been demonstrated 
by means of carefully controlled experiments for some 
of the crops mentioned in the above discussion, such as 
avocado and stone fruits, the data for other crops are 
based only on a close concomitance between chloride 
accumulation and observed leaf injury. 

Few instances of injury related to excessive sodium 
accumulation have been noted. With some crops 
sodium injury may be obscured by simultaneous chlo- 
ride injury, as Ayers and others (1951) have pointed 
out for avocado. In a water-culture study, Ayers 
(1950) observed leaf burn of avocado when leaves con- 
tained 0.5 percent sodium on a dry-weight basis. Lille- 



SALINE AND ALKALI SOILS 



65 



land and associates (1945) have indicated that sodium 
accumulation of 0.3 percent in almond leaves is asso- 
ciated with incipient leaf-burn symptoms. In sand 
cultures, Brown and coworkers (1953) have observed 
tipburn of Texas almond leaves containing 0.4 percent 
sodium and of plum leaves containing 0.3 percent. 
Unpublished data by Wadleigh and Gauch have indi- 
cated that leaf burn of salt-sensitive cotton varieties 
may occur in leaves containing 0.2 percent sodium. 

Chapman (1949) has indicated that chloride or 
sodium accumulations of 0.25 percent or higher in 
citrus leaves should be regarded as excessive. While 
these values are lower than those at which definite 
foliar injury may appear, they do emphasize the fact 
that under some conditions even lower values than those 
cited in the above discussion may indicate a definite 
tendency toward excessive accumulations of harmful 
ions in the plant. 

Foliar analysis is useful in the diagnosis of boron 
injury of many plant species. The boron content of 
normal, mature leaves of such plants as citrus, avo- 
cados, walnuts, figs, grapes, cotton, and of alfalfa 
tops is about 50 p. p. m. Boron contents of 20 p. p. m. 
or less indicate deficiency, while values above 250 
p. p. m. are usually associated with boron toxicity. 
Stone-fruit trees, apples, and pears do not accumulate 
high concentrations of boron in their leaves, although 
these species are sensitive to excess boron. If due al- 
lowance is made for varietal specificity in boron accumu- 
lation, foliar analysis may provide a readier basis for 
diagnosis than analysis of soil or water. 

Crop Selection for Saline Soils 

Because of saline irrigation water, high water table, 
or low permeability of the soil, it may not be econom- 
ically feasible to maintain low salinity. In such in- 
stances, the judicious selection of crops that can pro- 
duce satisfactory yields under saline conditions and the 
use of special management practices to minimize sa- 
linity may make the difference between success or 
failure. 

As has already been pointed out, the availability of 
water to plants is always a factor under saline con- 
ditions. For example, suppose alfalfa is being grown 
on a loam having a salt content of 0.2 percent sodium 
chloride and a wilting percentage of 6 when the latter 
is determined on a nonsaline sample. Under such con- 
ditions, because the osmotic effect is additive with soil- 
moisture tension, alfalfa will stop growing when the 
soil dries to a moisture content of only 13 percent. In 
other words, if the soil contains 0.2 percent salt, the 
alfalfa plant cannot use a large part of the soil moisture 
that is normally available under nonsaline conditions. 
The presence of even smaller quantities of salt in this 
soil would cause a fraction of the soil moisture above 
the wilting percentage to be unavailable to the plant. 
More frequent irrigation would be required to decrease 
the inhibitory effect of the salt on the growth of alfalfa. 

Although it has been shown that crop growth on 
saline soils is definitely benefited by more frequent 



irrigation, the need for this irrigation may not be indi- 
cated by the appearance of the crop (Richards and 
Wadleigh, 1952) . In nonsaline soils, there is usually a 
relatively abrupt transition from low moisture stress to 
high moisture stress conditions, and the wilting of the 
plant indicates the need for irrigation. In saline soils, 
changes in moisture stress are more gradual and, 
although the plants may be subjected to high stress, 
there is no abrupt transition in the turgor condition of 
the plant and, hence, no sign of the need for irrigation. 
Nevertheless, experiments have shown that crop growth 
is greatly improved by more frequent irrigation under 
such conditions. Careful leveling of the fields to insure 
more uniform moisture distribution during irrigation 
will also improve chances for successful crops on saline 
soils. 

Germination 

In selecting crops for saline soils, particular atten- 
tion should be given to the salt tolerance of the crop 
during germination because poor crops frequently re- 
sult from a failure to obtain a satisfactory stand. This 
problem is complicated by the fact that some crop 
species which are very salt tolerant during later stages 
of growth may be quite sensitive to salinity during 
germination (fig. 19). Sugar beets, for example, 
which are very salt tolerant during later stages of 
growth, are extremely sensitive during germination. 
On the other hand, barley has very good salt tolerance 
during all stages of growth, although it is more sensitive 
during germination than at later stages (Ayers and 
others, 1952) . Under field conditions, it is possible by 
modification of planting practices to minimize the ten- 
dency for salt to accumulate around the seed and to im- 
prove the stand of crops that are sensitive to salt dur- 
ing germination (Heald and coworkers, 1950) . 

Relative Salt Tolerance of Crop Plants 

The salt tolerance of many species and varieties of 
crop plants has been investigated at the Laboratory. 
Previously published lists (Magistad and Christiansen, 
1944, and Hay ward and Magistad, 1946) have been 
modified on the basis of recent findings and are pre- 
sented in table 8. 

The salt tolerance of a crop may be appraised ac- 
cording to three criteria: (1) The ability of the crop 
to survive on saline soils, (2) the yield of the crop on 
saline soils, and (3) the relative yield of the crop on a 
saline soil as compared with its yield on a nonsaline 
soil under similar growing conditions. Many previous 
observations on salt tolerance have been based mainly 
on the first criterion, ability to survive; but this method 
of appraisal has very limited practical significance in 
irrigation agriculture. Although it is recognized that 
the second criterion is perhaps of greater agronomic 
importance, the third criterion was used in compiling 
the present salt-tolerance lists because it provides a 
better basis of comparison among diverse crops. 

The salt-tolerance lists are arranged according to 
major crop divisions; and, in each division, crops are 



66 



AGRICULTURE HANDBOOK 60, U. S. DEPT. OF AGRICULTURE 



100 




I 5 9 13 17 

CONDUCTIVITY OF SATURATION EXTRACT - MILLIMHOS/CM. 

Figure 19.— Percent germination of four crops, as related to the conductivity of the saturation extract of the soil, under laboratory 

conditions (Ayers and Hayward, 1949). 



listed in three groups. Within each group, the crops 
are listed in the order of decreasing salt tolerance, 
but a difference of 2 or 3 places in a column may not 
be significant. EC B values given at the top of a column 
represent the salinity level at which a 50-percent de- 
crease in yield may be expected as compared to yields 
on nonsaline soil under comparable growing condi- 
tions. For example, for crops with high salt tolerance 
in the division of field crops, EC e values of 16 mmhos/ 
cm. occur at the top of the column and 10 mmhos/cm. at 
the bottom. This indicates that crops near the top of 
this column will produce about 50 percent as well on a 
soil having an EC e of 16 mmhos/cm. as on a nonsaline 
soil under similar conditions, and crops near the bottom 
of this column will produce about 50 percent as well 
on soils having an EC e of 10 mmhos/cm. as on a non- 
saline soil. EC e values having similar significance have 
been shown for each group of plants for which such 
data are available. 

In most instances, these data are based on a field-plot 
technique in which crops are grown on soils that are 
artificially adjusted to various salinity levels after the 
seedlings are established. By this method, crop yields 
were related to EC e values for comparable saline and 



nonsaline soils, and the salinity level associated with a 
50-percent decrement of yield was determined graphi- 
cally. In many of these studies, a number of varieties 
of a given crop were compared. Significant varietal 
differences were found for cotton, barley, and smooth 
brome, while for truck crops such as green beans, 
lettuce, onions, and carrots varietal differences were 
not of practical significance. 

In applying the information in the following table, 
it is important to remember that climatic conditions 
may influence profoundly the reaction of plants to 
salinity. The choice of suitable salt-tolerant varieties 
and strains will depend on local climatic factors; and, 
consequently, information on salt-tolerant varieties 
should be evaluated with reference to the conditions 
under which the crops are to be grown. The position 
of each crop in this table reflects its relative salt toler- 
ance under management practices that are customarily 
employed when this crop is grown under irrigation agri- 
culture and not the inherent physiological ability of 
the crop to withstand salinity under some given set of 
conditions that is uniform for all crops. 

A salt-tolerance list for some important crops of 
Holland has recently been prepared by Van den Berg 



SALINE AND ALKALI SOILS 



67 



Table 8. — Relative tolerance of crop plants to salt 1 



Field Crops 



Fruit Crops 



High salt tolerance 


Medium salt tolerance 


Low salt tolerance 


Date palm 


Pomegranate 


Pear 




Fig 


Apple 




Olive 


Orange 




Grape 


Grapefruit 




Cantaloup 


Prune 

Plum 

Almond 

Apricot 

Peach 

Strawberry 

Lemon 

Avocado 



Vegetable Crops 



#CeX10 3 = 12 


SC e X10 3 =10 


£C e X10 3 = 4 


Garden beets 


Tomato 


Radish 


Kale 

Asparagus 

Spinach 


Broccoli 

Cabbage 

Bell pepper 

Cauliflower 

Lettuce 

Sweet corn 

Potatoes (White 

Rose) 
Carrot 
Onion 
Peas 
Squash 
Cucumber 


Celery 
Green beans 


FC e X10 3 =10 


#C C X10 3 = 4 


EC e XlQ* = S 



Forage Crops 



M7 e X10 3 = 18 


#C C X10 3 =12 


£C e X10 3 = 4 


Alkali sacaton 


White sweetclover 


White Dutch 


Salt grass 


Yellow sweetclover 


clover 


Nuttall alkaligrass 


Perennial ryegrass 


Meadow foxtail 


Bermuda grass 


Mountain brome 


Alsike clover 


Rhodes grass 


Strawberry clover 


Red clover 


Rescue grass 


D alii s grass 


Ladino clover 


Canada wildrye 


Sudan grass 


Burnet 


Western wheat - 


Hubam clover 




grass 


Alfalfa (California 




Barley (hay) 


common) 




Bridsfoot trefoil 


Tall fescue 
Rye (hay) 
Wheat (hay) 
Oats (hay) 
Orchardgrass 
Blue grama 
Meadow fescue 
Reed canary 
Big trefoil 
Smooth brome 
Tall meadow oat- 
grass 
Cicer milkvetch 
Sourclover 
Sickle milkvetch 




EC e XlO z =12 


EC e X10* = 4 


#C e X10 3 = 2 



EC e X10* = 


= 16 


#C e X10 3 =10 


#C e X10 3 = 4 


Barley (grain) 
Sugar beet 
Rape 
Cotton 


Rye (grain) 
Wheat (grain) 
Oats (grain) 
Rice 


Field beans 






Sorghum (grain) 
Corn (field) 
Flax 








Sunflower 








Castorbeans 




EC e XlO* = 


= 10 


#C e X10 3 = 6 





1 The numbers following ECe X 10 3 are the electrical con- 
ductivity values of the saturation extract in miHimhos per 
centimeter at 25° C. associated with 50-percent decrease in 
yield. 

( 1950) . Based on field-plot studies in areas which had 
been inundated by salt or brackish water in 1944^-45, 
the salinity values ("salt index," expressed as grams 
NaCl per liter of soil water) associated with 75 percent 
of normal yields for 14 crops were determined. De- 
spite obvious differences in climate and cultural prac- 
tices, Van den Berg's results for relative salt tolerance 
are in good agreement with those in table 8. 

Relative Boron Tolerance of Crop Plants 

Plant species differ markedly in their tolerance to ex- 
cessive concentrations of boron. In sections where 
boron tends to occur in excess in the soil or irrigation 
water, the boron-tolerant crops may grow satisfactorily, 
whereas sensitive crops may fail. The relative boron 
tolerance of a number of crops was determined by Eaton 
(1935), and his results are reported in table 9 with 

Table 9. — Relative tolerance of plants to boron 

[In each group, the plants first named are considered as being more tolerant 

and the last named more sensitive] 



Tolerant 



Athel (Tamarix 

aphylla) 
Asparagus 
Palm (Phoenix 

canariensis) 
Date palm (P. dac~ 

tylifera) 
Sugar beet 
Mangel 
Garden beet 
Alfalfa 
Gladiolus 
Broadbean 
Onion 
Turnip 
Cabbage 
Lettuce 
Carrot 



Semi tolerant 



Sunflower (native) 

Potato 

Acala cotton 

Pima cotton 

Tomato 

Sweetpea 

Radish 

Field pea 

Ragged Robin rose 

Olive 

Barley 

Wheat 

Corn 

Milo 

Oat 

Zinnia 

Pumpkin 

Bell pepper 

Sweetpotato 

Lima bean 



Sensitive 



Pecan 

Black walnut 

Persian (English) 
walnut 

Jerusalem arti- 
choke 

Navy bean 

American elm 

Plum 

Pear 

Apple 

Grape (Sultanina 
and Malaga) 

Kadota fig 

Persimmon 

Cherry 

Peach 

Apricot 

Thornless black- 
berry 

Orange 

Avocado 

Grapefruit 

Lemon 



68 



AGRICULTURE HANDBOOK 60, U. S. DEPT. OF AGRICULTURE 



minor modifications based on field observations. The 
boron-tolerance lists are analogous to the salt-tolerance 
lists and subject to much the same limitations in inter- 
pretation. Differences in position of a few places may 
or may not be significant, and there is no sharp divi- 
sion between successive classes. Climate and variety 
may also be factors in altering the indicated tolerance 
of a given species under specific conditions. 

Available information on boron tolerance does not 
permit the establishment of definite permissible limits 
of boron concentration in the soil solution. Irrigation 



waters are classified on the basis of boron content in 
table 14, chapter 5, with reference to sensitive, semi- 
tolerant, and tolerant crops. The effect of a given con- 
centration of boron in the irrigation water on the boron 
content of the soil solution will be conditioned by soil 
characteristics and management practices that influence 
the degree of boron accumulation in the soil. In the 
discussion of saturation extracts of soils (ch. 2), 0.7 
p. p. m. boron in the saturation extract was indicated 
as the approximate safe limit for sensitive crops. 



Chapter 5 



Quality of Irrigation Water 



The concentration and composition of dissolved con- 
stituents in a water determine its quality for irrigation 
use. Quality of water is an important consideration in 
any appraisal of salinity or alkali conditions in an 
irrigated area. Much work has been done on quality 
of irrigation water. The United States Geological Sur- 
vey is very active in general quality-of-water studies, 
and the analyses made by this agency are published at 
irregular intervals in the USGS Water-Supply Papers. 
In addition to current programs, analyses dating back 
to the beginning of irrigation in the western United 
States are recorded in this series. The Geological Sur- 
vey took the leadership in preparing an index of water 
analyses that has proved to be very useful. 13 Agricul- 
tural experiment stations in the Western States have 
also been active in quality-of-water studies and have 
published a number of bulletins on this subject (Smith, 
1949; Smith and others, 1949; Miller, 1950; Jensen 
and others, 1951; Thorne and Thorne, 1951) . 

The Rubidoux Laboratory since 1928 has analyzed 
more than 22,000 samples of irrigation water. Much 
of the information has been published, and all of it is 
available in the records of the Laboratory. This work 
shows that poor quality of both surface and ground 
waters is a limiting factor in the irrigation of many 
areas in this country and abroad. 

There are many places in western United States, par- 
ticularly in the desert areas of California, Arizona, 
Texas, and New Mexico, and also in the other parts 
of the world, where ground water is available but the 
quality is questionable or unsatisfactory. Similarly, 
where surface waters are used, the present rate of in- 
crease of irrigation development and changes in man- 
agement practices are resulting in serious quality-of- 
water problems. There is the tendency to divert for 
irrigation all of the available water. This means that 
over a period of years the downstream diversions may 
change from uncontaminated river water to a substan- 
tial proportion of drainage return-flow of poor quality. 
To cope with such problems, it is necessary to have de- 
tailed information concerning the quality of irrigation 
water and a background of experience relating to the 
effect of irrigation waters on soils and crops. 



13 U. S. Department of the Interior, Geological Survey. 

INVENTORY OF PUBLISHED AND UNPUBLISHED CHEMICAL ANALYSES 
OF SURFACE WATERS IN THE WESTERN UNITED STATES, NOTES ON 

hydrologic activities. Bui. No. 2, October 1948. [Processed.] 



Methods of Analysis 

The methods used by this Laboratory for the analysis 
of irrigation waters are given in chapter 8, Methods 70 
to 86. The Versenate titration (Method 79) for cal- 
cium plus magnesium, the flame photometer method for 
sodium and potassium (Methods 80b and 81c) , and the 
colorimetric method for boron (Method 73b), make 
possible rapid determinations without sacrificing 
accuracy. Also, the volume of water required for an 
analysis is less, thus simplifying the collection and 
transportation of samples. 

If all of the principal constituents have been deter- 
mined and expressed in chemical equivalents, the sum 
of the cations should equal the sum of the anions, and 
a lack of balance indicates an error. There are a num- 
ber of ways in which a water analysis can be checked. 
The numerical value of the ratio — electrical conduc- 
tivity in micromhos per centimeter divided by cations 
in milliequivalents per liter — should be about 100 for 
most waters (fig. 20) . This ratio may be as low as 80 
for bicarbonate or sulfate waters in which calcium and 
magnesium are high, but for chloride waters that are 
high in sodium the ratio may be as high as 110. The 
numerical value of the ratio — dissolved solids in parts 
per million divided by conductivity in micromhos per 
centimeter — should be approximately 0.64 (fig. 21). 
A third ratio — dissolved solids in parts per million 
divided by cations in milliequivalents per liter — has a 
value of approximately 64. These values are averages 
based on a large number of determinations for natural 
waters. 

Characteristics That Determine Quality 

The characteristics of an irrigation water that appear 
to be most important in determining its quality are: 
(1) Total concentration of soluble salts; (2) relative 
proportion of sodium to other cations; (3) concentra- 
tion of boron or other elements that may be toxic ; and 
(4) under some conditions, the bicarbonate concentra- 
tion as related to the concentration of calcium plus 
magnesium. 

Electrical Conductivity 

The total concentration of soluble salts in irriga- 
tion waters can be adequately expressed for purposes of 
diagnosis and classification in terms of electrical con- 

69 



70 



AGRICULTURE HANDBOOK 60, U. S. DEPT. OF AGRICULTURE 



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8 100 



8 1000 



CONDUCTIVITY 



MICROMHOS /CM.(ECxl0 6 ) AT 25° C. 



Figure 20. — Concentration of irrigation waters in milliequivalents per liter of cations as related to conductivity. 



ductivity. The conductivity is useful because it can be 
readily and precisely determined. 

Nearly all irrigation waters that have been used 
successfully for a considerable time have conductivity 
values less than 2,250 micromhos/cm. Waters of 
higher conductivity are used occasionally, but crop pro- 
duction, except in unusual situations, has not been 
satisfactory. 

Saline soils are those in which the conductivity of 



the saturation extract is greater than 4 millimhos/cm., 
or 4,000 micromhos/cm. It has been found that the 
conductivity of the saturation extract of a soil, in the 
absence of salt accumulation from ground water, usually 
ranges from 2 to 10 times as high as the conductivity 
of the applied irrigation water. This increase in the 
salt concentration is the result of continual moisture 
extraction by plant roots and evaporation. Therefore, 
the use of waters of moderate to high salt content may 



SALINE AND ALKALI SOILS 



71 



result in saline conditions, even where drainage is satis- 
factory. In general, waters with conductivity values 
below 750 micromhos/cm. are satisfactory for irriga- 
tion insofar as salt content is concerned, although salt- 
sensitive crops may be adversely affected by the use of 
irrigation waters having conductivity values in the 
range 250 to 750 micromhos/cm. 

Waters in the range of 750 to 2,250 micromhos/cm. 
are widely used, and satisfactory crop growth is ob- 
tained under good management and favorable drainage 
conditions, but saline conditions will develop if leaching 



and drainage are inadequate. Use of waters with con- 
ductivity values above 2,250 micromhos/cm. is the ex- 
ception, and very few instances can be cited where such 
waters have been used successfully. Only the more salt- 
tolerant crops can be grown with such waters and then 
only when the water is used copiously and the subsoil 
drainage is good. 

As discussed in chapter 3, the steady-state leaching 
requirement for soils where no precipitation of salts 
occurs is directly related to the electrical conductivity 
of the irrigation water and the permissible conductivity 



5000 



• 

2 


1000 


a: 
q: 


8 



< 
a: 

*- 

UJ 

o 

z 
o 
o 



100 
8 

6 
5 




^^^t^«ai^i6ttiid»i 



SURFACE STREAM 




8 1000 



CONDUCTIVITY 



MICR0MH0S /CM. (ECxIO 6 ) AT 25*0. 



Figure 21.— Concentration of irrigation waters in parts per million as related to conductivity. 



72 



AGRICULTURE HANDBOOK 60, U. S. DEPT. OF AGRICULTURE 



of the water draining from the root zone. The leach- 
ing requirements for specified electrical conductivity 
values of the irrigation and drainage waters, as deter- 
mined from equation 2, chapter 3, are given in table 10. 

Table 10. — Leaching requirement 1 as related to the 
electrical conductivities of the irrigation and drain- 
age waters 



Electrical 
conductivity 
of irrigation 


Leaching requirement for the indicated maxi- 
mum values of the conductivity of the drain- 
age water at the bottom of the root zone 


waters 
(micromhos/ 

cm.) 


4 mmhos/ 
cm. 


8 mmhos/ 
cm. 


12 mmhos/ 
cm. 


16 mmhos/ 
cm. 


100 


Percent 

2.5 

6.2 

18.8 

56.2 


Percent 

1.2 

3.1 

9.4 

28.1 

62.5 


Percent 

0.8 

2.1 

6.2 

18.8 

41.7 


Percent 
0.6 


250 


1.6 


750 


4.7 


2,250 

5 000 


14.1 
31.2 









1 Fraction of the applied irrigation water that must be 
leached through the root zone expressed as percent. 

Although, for reasons stated in chapter 3, these 
leaching requirement values are probably somewhat 
high, they illustrate the manner in which the electrical 
conductivity of irrigation waters influences the leaching 
requirement under various levels of soil salinity, ex- 
pressed in terms of electrical conductivity of the soil 
solution at the bottom of the root zone. It is ap- 
parent that the water-transmission and drainage prop- 
erties of the soil and the salt tolerance of the crop to be 
grown are important factors in appraising irrigation 
waters from the standpoint of total salt concentration. 

Sodium-Adsorption-Ratio 

The soluble inorganic constituents of irrigation 
waters react with soils as ions rather than as molecules. 
The principal cations are calcium, magnesium, and 
sodium, with small quantities of potassium ordinarily 
present. The principal anions are carbonate, bicar- 
bonate, sulfate, and chloride, with fluoride and nitrate 
occurring in low concentrations. The alkali hazard 
involved in the use of a water for irrigation is deter- 
mined by the absolute and relative concentrations of 
the cations. If the proportion of sodium is high, the 
alkali hazard is high; and, conversely, if calcium and 
magnesium predominate, the hazard is low. The im- 
portance of the cationic constituents of an irrigation 
water in relation to the chemical and physical proper- 
ties of the soil was recognized even before cation ex- 
change reactions were widely understood. Scofield and 
Headley (1921) summarized the results of a series of 
alkali reclamation experiments with the statement: 
"Hard water makes soft land and soft water makes 
hard land." Alkali soils are formed by accumulation 
of exchangeable sodium and are often characterized by 
poor tilth and low permeability. 



In the past the relative proportion of sodium to other 
cations in an irrigation water usually has been ex- 
pressed in terms of the soluble-sodium percentage. 
However, as was shown in chapter 2, the sodium-ad- 
sorption-ratio of a soil solution is simply related to 
the adsorption of sodium by the soil; consequently, 
this ratio has certain advantages for use as an index of 
the sodium or alkali hazard of the water. This ratio 
is defined by the equation : 

SAR = Na + / V(Ca ++ + Mg ++ )/2 

where Na + , Ca ++ , and Mg ++ represent the concentrations 
in milliequivalents per liter of the respective ions. A 
nomogram for estimating the SAR value of an irriga- 
tion water is shown in figure 22. This nomogram is 
similar to figure 27, but figure 22 has scales more 
suitable for the cationic concentrations encountered in 
irrigation waters. 

An ESP scale is included in the nomogram opposite 
the SAR scale. This ESP scale is based on the regres- 
sion line shown in figure 9, chapter 2, in which the 
relation between SAR and ESP was given as 

100 (-.0126 +.01475 SAR) 



ESP= 



1 + 



(-.0126 + .01475 SAR) 

This empirical equation was used to relate the ESP 
scale to the SAR scale in figure 22. After the SAR 
value of an irrigation water is determined by use of the 
nomogram, it is possible from the central scale to esti- 
mate the ESP value of a soil that is at equilibrium with 
the irrigation water. It is to be expected, however, that 
this condition would not often occur in the field, be- 
cause the soil solution is nearly always appreciably 
more concentrated than the irrigation water. 

The concentration of the soil solution is increased 
by the extraction of water from the soil by roots and by 
evaporation. As the quantity of salt absorbed by 
plants is relatively small, the solution remaining in the 
soil is more concentrated than the applied irrigation 
water. At the next irrigation this more concentrated 
solution may be displaced downward or diluted, and 
so the concentration of the solution in contact with 
the soil varies with time and location in the profile. It 
is not unusual to find shallow ground water or drain- 
age water that is from 2 to 10 times as concentrated as 
the irrigation water. It is reasonable to assume, how- 
ever, that for a limited depth of soil, such as the top 
12 inches, the concentration of the soil solution is not, 
on the average, more than 2 or 3 times the concentration 
of the irrigation water. 

Under conditions in soil where it is permissible to 
neglect precipitation and absorption of soluble salts 
by roots, it is clear that irrigation water, after entering 
the soil, becomes more concentrated without change in 
relative composition, i. e., the soluble-sodium percent- 
age does not change. The SAR value, however, in- 
creases in proportion to the square root of the total 
concentration, i. e., if the concentration is doubled the 
SAR value increases by a factor of 1.41. If the concen- 
tration is quadrupled the SAR value will be doubled. 



SALINE AND ALKALI SOILS 



73 
Ca 4+ + Mg+ + 




Figure 22.— Nomogram for determining the SAR value of irrigation water and for estimating the corresponding ESP value of 

a soil that is at equilibrium with the water. 



259525 O - 54 - 6 



74 



AGRICULTURE HANDBOOK 60, U. S. DEPT. OF AGRICULTURE 



It has been observed that where an irrigation water of 
relatively constant composition is used and drainage 
conditions are good, the ESP value of soil varies only 
slightly from season to season or from year to year. 
This implies that the cation-exchange material of the 
soil has reached a steady state relative to the cations 
in the soil solution which are derived from the irriga- 
tion water. All suitable data bearing on the relation- 
ship between the soluble cations of the irrigation water 
and the exchangeable cations of the soil have been as- 
sembled from the records of the Laboratory. Only 

24 



those instances were selected in which the drainage was 
known to be good and only the surface sample of soil 
from each site was considered. It was further required 
that the composition of the irrigation water be relatively 
invariant with time and that the water must have been 
used for many seasons in the field experiments or for 
many irrigations in experiments conducted at the 
Laboratory. 

The relation between the SAR value of the irrigation 
waters and the ESP values of the soil samples is shown 
by the points on the graph in figure 23. The solid 



< 



UJ 
O 

<r 

UJ 

o. 
i 



16 



/ 



/ 



o 

co 12 
i 

UJ 

-J 

ID 

< 
UJ 

© 8 



o 

X 

UJ 




eeo 100 (-0.012 6 4-0.01475 



I +(-0.0126 +0.01475 • 



4 8 

SODIUM- ADSORPTION 



12 16 

RATIO OF IRRIGATION 



20 
WATER 



24 



Figure 23.— The exchangeable-sodium-percentage volues of samples of surface soil as related to the sodium-adsorption-ratio values 
of the irrigation waters: 0, small lysimeters after 42 irrigation cycles; +, large lysimeters after prolonged leaching; •, field 
observations. 



SALINE AND ALKALI SOILS 



75 



curve represents the relation between SAR and ESP 
given by the equation shown in the figure, and also in- 
dicated by scales C and D in the nomogram of figure 

22. It is apparent that, under the conditions existing 
in the field, the ESP values of the soil samples are 
generally higher than the estimated values. The devia- 
tions from the solid curve are undoubtedly owing to the 
fact that the concentrations of the soil solutions are 
somewhat higher than the concentrations of the irriga- 
tion waters. 

The dotted curve in figure 23 shows the ESP values 
that would be attained by the soils, assuming a three- 
fold increase in the concentration of the irrigation 
waters. In other words, if the soluble-sodium percent- 
ages of the irrigation waters after entering the soils 
remain unchanged but the total concentrations increase 
by a factor of 3, the SAR values would increase by a 
factor equal to the square root of 3 and the resulting 
predicted ESP values for the samples would lie along 
the dotted curve in the figure. The distribution of the 
points on the graph that represent the field samples indi- 
cates that the saturation extracts were 1 to 3 times as 
concentrated as the irrigation waters applied. 

More data are needed to explain the relation of ex- 
changeable sodium to water quality and irrigation prac- 
tices. On the basis of the relationship shown in figure 

23, SAR appears to be a useful index for designating the 
sodium hazard of waters used for irrigation. 

Boron 

Boron is a constituent of practically all natural 
waters, the concentration varying from traces to several 
parts per million. It is essential to plant growth, but is 
exceedingly toxic at concentrations only slightly above 
optimum. Eaton (1944) found that many plants made 
normal growth in sand cultures with a trace of boron 
(0.03 to 0.04 p. p. m.), and that injury often occurred 
in cultures containing 1 p. p. m. 

Bicarbonate 

In waters containing high concentrations of bicar- 
bonate ion, there is a tendency for calcium and magnes- 
ium to precipitate as carbonates as the soil solution be- 
comes more concentrated. This reaction does not go to 
completion under ordinary circumstances, but insofar 
as it does proceed, the concentrations of calcium and 
magnesium are reduced and the relative proportion of 
sodium is increased. Eaton (1950) uses three terms in 
connection with this reaction: 

( 1 ) Soluble-sodium percentage "found" = ( Na + X 100 ) / 
(Ca ++ + Mg ++ + Na + ) ; (2) Soluble-sodium percentage 
"possible" = (Na + X100)/((Ca ++ + Mg ++ + Na + ) - 
(CO3- + HCO3-) ), where the C0 3 - + HC0 3 - deduction 
does not exceed Ca ++ + Mg ++ ; (3) "Residual Na 2 C0 3 " = 
(C(V- + HC(V) - (Ca ++ + Mg ++ ). 
In these relations the ionic constituents are expressed 
as milliequivalents per liter. 

The influence of the bicarbonate ion concentration 
of irrigation waters upon the exchangeable-sodium- 
percentage has been studied at the Laboratory. One 



experiment involved the growth of Rhodes grass in pots 
of Hanford loam soil. The soils were irrigated with the 
waters under test, then allowed to dry to a soil-moisture 
tension of about 700 to 800 cm. of water between irriga- 
tions. There were low- and high-leaching treatments. 
The high-leaching treatment provided for the applica- 
tion of excess irrigation water so that about 25 percent 
of the applied irrigation water was collected as per- 
colate after each irrigation. The low-leaching regime 
provided for the same proportion of leachate every 
fourth irrigation. Exchangeable-sodium-percentages 
were somewhat greater with the low-leaching treat- 
ments than with the high. Table 11 describes the irriga- 
tion waters that were tested and reports the results of 
the analyses of soil samples from the low-leaching 
treatments. The soil samples were collected after the 
42d and 86th irrigations. 

The use of two of the bicarbonate waters, 20b and 
10b, gave rise to substantially higher ESP values than 
the corresponding chloride waters, 20a and 10a (table 
11 ) . At the end of 42 irrigations, there was no appreci- 
able difference between the 5a and 5b waters, but a 
significant difference was found after the 86th irriga- 
tion. With the remaining waters, there appears to be 
no difference between the chloride and bicarbonate 



treatments. 



Typical Waters 



The analyses of a group of surface waters from 
western United States that are typical of the waters that 
are being used for irrigation purposes are presented in 
table 12. The composition of a surface water may vary 
considerably, but the analyses shown were selected to 
represent average conditions. 

Ground waters are much more variable in composi- 
tion than surface waters. With few exceptions, it is not 
possible to select ground waters that are typical of an 
area or to generalize about the ground waters of a given 
basin. Analyses of samples from a large number of 
wells in the Coachella Valley in Riverside County, Cali- 
fornia, illustrate this point. Electrical conductivity 
varies from 208 to 13,200 micromhos/cm ; boron from 
a trace to 3.15 p. p. m., and soluble-sodium percentage 
(SSP) from 21 to 97. Even where wells are only a 
short distance apart or are pumping from different 
strata, great variation is sometimes noted. Two wells 
within a half mile of each other had conductivities of 
13,200 and 604 micromhos/cm., and 3.03 and 0.38 
p. p. m. boron, respectively. The first of these wells is 
565 feet deep and the second 180 feet deep. The quality 
of the water from different strata tapped by the same 
well may vary, or the quality may change with length of 
time of pumping. This change with time is usually 
associated with overpumping but it does not often 
occur. The quality of water from a new well should 
be determined prior to its use for irrigation. 

Classification of Irrigation Waters 

In classification of irrigation waters, it is assumed 
that the water will be used under average conditions 



76 



Table 11. 



AGRICULTURE HANDBOOK 60, U. S. DEPT. OF AGRICULTURE 

The composition of the irrigation waters used and the analyses of soil samples from a bicarbonate 
experiment at the Laboratory; low-leaching noncalcareous treatments 







Irriga 


don watet 












Analyses of soil samples collected after — 






Irrig. 


Concen- 
tration 


Composition 


Residual 
Na2COa 


Irrigation No. 42 


Irrigation No. 86 


water 
No. 


Ca++ 


Na + 

Percent 

75 
75 


hco 3 - 


ci- 


J5CXMX 
at25°C. 


pH, 


ES 


ESP 


EC, X10» 
at 25° C. 


pH. 


ES 


ESP 


20a 
20b 


Meq./I. 
20.0 

20.0 


Percent 
25 
25 


Percent 

50 


Percent 
100 
50 


Meq.jl. 

5.0 


3.73 

5.94 


6.8 
8.6 


Meq./ 
100 gm. 
1.16 
4.52 


12 
52 


5.30 

16.0 


6.8 
9.4 


Meq./ 
100 gm. 
1.40 
6.45 


16 

72 


10a 
10b 


10.0 
10.0 


25 
25 


75 

75 



50 


100 
50 



2.5 


2.22 
2.03 


7.2 
8.6 


.80 
1.72 


8.4 
20 


3.70 
7.30 


7.3 
9.0 


1.40 
3.80 


15 
42 


5a 
5b 


5.0 
5.0 


25 

25 


75 
75 



50 


100 
50 



1.25 


1.28 
1.18 


6.8 
8.4 


.84 
1.02 


9.0 
10 


1.78 
2.42 


6.7 

7.7 


1.12 
1.98 


11 
20 


la ... 
lb 


1.0 
1.0 


25 
25 


75 
75 



50 


100 
50 



.25 


.40 
.36 


7.1 
7.0 


.22 
.24 


2.4 
2.6 


.32 
.34 


6.4 
6.4 


.25 

.22 


2.4 
2.1 


5aL. . . . 
5bL. . . . 


5.0 
5.0 


75 

75 


25 
25 



85 


100 
15 



.50 


1.02 
.69 


6.9 
8.1 


.22 
.29 


2.2 
3.1 


1.50 
1.05 


6.1 

7.4 


.23 
.36 


2.2 
3.5 


laL. . . . 
IbL... 


1.0 

1.0 


75 
75 


25 
25 



85 


100 
15 



.10 


.34 
.33 


7.0 

7.2 


.14 
.14 


1.5 
1.4 


.36 
.34 


6.4 
6.4 


.12 
.13 


1.1 
1.3 



with respect to soil texture, infiltration rate, drainage, 
quantity of water used, climate, and salt tolerance of 
crop. Large deviations from the average for one or 
more of these variables may make it unsafe to use what, 
under average conditions, would be a good water; or 
may make it safe to use what, under average conditions, 
would be a water of doubtful quality. This relationship 
to average conditions must be kept in mind in connec- 
tion with the use of any general method for the classifi- 
cation of irrigation waters. 

A diagram for classifying irrigation waters was sug- 
gested by Wilcox (1948), and this was subsequently 
modified by Thorne and Thorne (1951) for the classifi- 
cation of the irrigation waters of Utah. Both diagrams 
have been widely used. In the classification presented 
below, certain features of both diagrams are used. 
However, the SAR value rather than the soluble-so- 
dium percentage is taken as the index of sodium status 
or sodium hazard. 

Salinity Hazard 

Waters are divided into four classes with respect to 
conductivity, the dividing points between classes being 
at 250, 750, and 2,250 micromhos/cm. (See figure 
25). These class limits were selected in accordance 
with the relationship between the electrical conductivity 
of irrigation waters and the electrical conductivity of 
saturation extracts of soil as discussed previously in this 
chapter under the heading, Electrical Conductivity. 
The frequency distribution of the electrical conductivity 
of three groups of irrigation waters with respect to 
these four classes has been determined on the basis of 
number of water sources and acreage irrigated. These 
three groups of data were compiled from the following 
sources : 



Group 1. Data from Laboratory files for 1,142 ir- 
rigation water sources, both surface and ground 
water. 

Group 2. Data estimated from figure 1, page 10, of 
Utah Agr. Expt. Sta. Bui. 346; Irrigation Waters 
of Utah, by Thorne and Thorne (1951). 

Group 3. All conveniently available data from pro- 
jects irrigated with surface waters of known and 
reasonably constant composition. 

The frequency distribution of the first two groups is 
with respect to the number of sources, while distribu- 
tion of the third group is with respect to acres irrigated. 
These data are presented in table 13. The frequency- 
distribution curves for the first two groups of waters are 
shown in figure 24. 

It is apparent that more than half of the waters con- 
sidered in table 13 have conductivity values below 750 
micromhos/cm., the lowest limit used in the earlier 
schemes of classification. The establishment of a class 
limit at 250 micromhos/cm. further divides this large 
group. Considering the first group of data, 11 percent 
of the sources had conductivity values below 250 
micromhos/cm. and are in the low-salinity class. The 
waters of the medium-salinity class have conductivities 
of 251 to 750 micromhos/cm. and comprise 47 percent 
of the sources. The remaining 42 percent represent 
irrigation waters of high or very high salinity. Distri- 
bution of waters in group 2 is similar to those in 
group 1. 

Sodium Hazard 

The establishment of water-quality classes from the 
standpoint of the sodium hazard is more complicated 
than for the salinity hazard. The problem can be ap- 
proached from the point of view of the probable ex- 



Table 12. —Chemical composition of some river waters used for irrigation in western United States l 



River 



Location 



Missouri » | Williston, N. Dak . 

Yellowstone . . . 
North Platte 2. 

South Platte . . 
Platte 



Arkansas. . 
Do*. . 
Canadian s . 



Rio Grande. 

Do 

Do 

Pecos 2 



Miles City, Mont , 
Wyoming-Nebraska lines . 

Englewood, Colo 

Aurora, Nebr 



Gila 

Salt 

Colorado , 



Sevier 6 . . . . . 
Do*.... 

Weber 

Humboldt 7 . 

Sacramento . 
Kern 



La Junta, Colo 

Ralston, Okla 

Conchos Dam, N. Mex. 

Otowi Bridge, N. Mex . 

El Paso, Tex 

Roma, Tex 

Carlsbad, N. Mex 



Florence, Ariz ■ 

Stewart Mountain Dam, Ariz 
Yuma, Ariz 



Columbia . 



Snake B 

Payette «. . . . 



Central, Utah .... 

Delta, Utah 

Ogden, Utah 

Rye Patch, Nev . . 

Tisdale, Calif. . . . 
Baker afield, Calif. 



Rogue. . 



Wenatchee, Wash 

Minidoka, Idaho .... 
Black Canyon, Idaho, 

Medford, Oreg 



Date 
sampled 



11/29/45 

7/22/48 
10/8/45 

7/11/44 
7/21/51 

7/21/44 

8/16/44 

6/3/43 

6/46 

6/46 

6/46 

1945/46 

4/10/34 

3/8/34 

3/21/43 

6/5/49 

6/3/49 

10/7/49 

8/48 

8/15/47 
9/28/44 

11/25/35 

1948/49 
1948/49 

9/13/32 



ECX10* 
at 25° C. 



838 
548 
828 
406 
800 

1,210 

1,670 

844 

340 
1,160 

607 
3,210 

1,720 
1,210 
1,060 

580 

2,400 

510 

1,173 

162 
234 

151 

410 
100 

108 



Dis- 
solved 
solids 



P. p. m. 
574 
368 
565 
246 
571 

981 
967 
586 

227 

754 

380 

2,380 

983 
664 
740 

338 

1,574 

308 

8 658 

108 
152 

»78 

8 246 
8 60 

72 



Sum of 
cations 



Boron 



Meq.j I. 
9.48 
5.71 
8.99 
4.07 
7.98 

14.38 

14.52 

9.57 

3.39 
11.54 

5.76 
38.00 

16.85 
11.27 
10.96 

5.47 
25.81 

5.58 
11.55 

1.73 
2.36 

1.48 

4.54 
.91 

1.15 



P. p. m. 
0.1 
.11 
.1 
.03 
.12 

.11 




26 
10 
10 

11 

46 

.03 

.62 

.05 
.20 

.05 



09 



Ca 



3.49 
2.27 
3.59 
1.84 
2.96 

7.18 
4.34 
3.64 

1.86 

4.16 

2.49 

17.27 

3.59 
2.38 
4.79 

2.50 
3.14 
3.32 
1.75 

.66 
1.00 

.90 

2.15 
.40 

.54 



Mg 



2.38 
1.22 
1.64 
.87 
1.67 

3.49 
2.14 
2.63 

.70 
1.42 

.86 
9.21 

1.99 
1.20 
2.11 

1.23 
6.90 
1.44 
1.89 

.57 
.24 

.39 

1.29 
.23 

.26 



Milliequivalents per liter 



Na 



3.48 


0.13 


2.11 


.11 


3.61 


.15 


1.28 


.08 


3.35 




3.47 


.24 


8.04 


3. 


30 



.83 
5.96 
2.41 
11.52 



11.27 
7.69 
4.06 



1.57 

15.31 

.73 

7.91 

.45 
1.06 

.19 

.84 
.18 

.33 



.17 
.46 
.09 



.05 
.06 



.26 
.10 

.02 



COs 





(*) 


.10 
.20 

( 3 ) 







( 3 ) 

0* 




05 



.20 
.39 

( 3 ) 

.10 
.33 
.42 









34 








HCOs 



3.54 
2.40 
4.46 
1.99 
2.85 

3.95 
2.79 

2.72 

1.77 
3.59 
2.03 
3.18 

3.68 
2.40 
2.64 

4.10 
4.76 
3.66 
5.20 

1.35 
1.51 

1.26 

2.59 
.63 

.85 



SO4 



5.39 
2.96 
3.98 
1.21 
4.56 

9.80 
4.39 
6.33 

1.50 

5.00 

1.88 

23.11 

3.26 

.85 

6.39 

1.12 

8.44 

.82 

2.17 

.14 
.49 

.21 

.91 
.18 

(>) 



CI 



0.34 
.15 
.54 
.69 
.76 

.62 

7.28 

.51 

.14 

3.10 

1.88 

11.99 

9.95 
7.65 
2.05 

.74 

12.52 

.54 

4.46 

.20 
.40 

.07 

.74 
.12 

.25 



SSP 



37 
37 
40 
31 
42 

24 
55 

34 

24 
52 
42 
30 



13 

19 
20 

29 



SAR 



2.0 
1.6 
2.2 
1.1 
2.2 

1.5 

4.5- 
1.9 

.7 
3.6 
1.9 
3.2 



67 


6.7 


68 


5.7 


37 


2.2 


29 


1.1 


59 


6.8 


13 


.5 


68 


5.9 


26 


.6 


45 


1.3 



.2 

.6 
.3 



Residual 
Na 2 C03 



Meq.fl. 


































47 












1. 


56 




12 


• 


27 

















• 


05 



6 After 



1 Except as noted, these analyses were made by the Rubidoux Unit, U. S. Salinity Laboratory Riverside, California. J After U. S. Geol Survey (1950). 
erU S. Geol. Survey (1945). » After Thome and Thome (1951). ' After Miller (1950). • Calculated. • After Jensen and others (1951). 



3 Trace. * After U. S. Geol. Survey (1949). 



78 



AGRICULTURE HANDBOOK 60, V. S. DEPT. OF AGRICULTURE 



200 



II 



PERCENT IN EACH CONDUCTIVITY CLASS 
47 33 9 



o 

z 

UJ 

o 

UJ 

u. 



100- 











NUMBER^ 1142 










MEDIAN = 613 


/ 




1 


1 


MEAN = 934 






1000 


2000 


' ^sBoo^^Tdoo^^ 



250 750 2250 

CONDUCTIVITY — 



MICROMHOS/CM. 



DATA FROM LABORATORY FILES 



tooo 



200 



PERCENT IN EACH CONDUCTIVITY CLASS 

33 12 



o 

z 

UJ 

o 

UJ 




250 



1000 
750 



2000 
2250 



3000 



4000 



CONDUCTIVITY — MICROMHOS/CM. 



5000 



DATA FROM THORNE AND THORNE (1951) 

Figure 24. — Frequency distribution of two groups of irrigation waters with respect to electrical conductivity. 



SALINE AND ALKALI SOILS 



79 



Table 13.— Distribution of 3 groups of irrigation 
waters among 4 concentration classes 



Conductivity- 
range (micro- 
mnos/cm. 

at 25° C.) 


Group 1 


Group 2 


Group 3 


Sam- 
ples 


Per- 
cent 


Sam- 
ples 


Per- 
cent 


Acres 


Per- 
cent 


<250 


Num- 
ber 
124 
541 
378 
99 


11 

47 

33 

9 


Num- 
ber 
15 
105 
71 
26 


7 
48 
33 
12 


Thou- 
sands 
453 
977 
671 
22 


21 


251-750 

751-2,250 

2,251-5,000 ...... 


46 

32 

1 


Total 


1,142 


100 


217 


100 


2,123 


100 



tent to which soil will adsorb sodium from the water 
and the rate at which adsorption will occur as the water 
is applied. Consider the simple case where a nonalkali 
soil is leached continuously with a high-sodium irriga- 
tion water and an increase in concentration of the salts 
in the solution is prevented by the absence of plant 
growth and of surface evaporation. Under these con- 
ditions the ESP which the soil will attain when it and 
the water are in equilibrium can be predicted approxi- 
mately from the SAR value of the water; the rate at 
which the equilibrium condition will be attained will 
depend on the total cation concentration or electrical 
conductivity of the water. Thus, for this situation, ap- 
plication of waters having the same sodium-adsorption- 
ratio and variable electrical conductivities would ulti- 
mately result in about the same exchangeable-sodium- 
percentages, but the amount of water required to bring 
the soil to this ultimate exchangeable-sodium-per- 
centage would vary inversely with the electrical con- 
ductivity. In actual practice, the SAR value of the 
water increases in the soil, owing to the increase in con- 
centration of all salts and the possible precipitation 
of calcium and magnesium salts as the moisture content 
is decreased by plant extraction and surface evapora- 
tion. This results in a somewhat higher ESP than 
would be predicted directly from the SAR value of the 
water (fig. 23). Although the SAR value is the best 
available index of the equilibrium ESP of soil in rela- 
tion to irrigation water, total cation concentration or 
conductivity is an additional factor and is taken into 
account in the following classification of sodium 
hazard. 

Diagram for Classifying Irrigation Waters 

The diagram for the classification of irrigation waters 
is shown in figure 25 and is based on the electrical con- 
ductivity in micromhos per centimeter and the sodium- 
adsorption-ratio. 

In earlier diagrams curves representing mass-action 
equations between soluble and exchangeable cations de- 
limited the several sodium classes. The curves in figure 
25 can be constructed by the use of the following 
empirical equations : 



Upper curve: S = 43.75-8.87 (log C) ; 
Middle curve: S = 31.31-6.66 log C) ; 
Lower curve: S= 18.87 — 4.44 (logC) ; 

Where 5 = sodium-adsorption-ratio; C — electrical con- 
ductivity in micromhos per centimeter; log = loga- 
rithm to base 10. 

These equations plot as straight lines on rectangular 
coordinate paper when log C is used. 

The curves are given a negative slope to take into 
account the dependence of the sodium hazard on the 
total concentration. Thus, a water with a SAR value 
of 9 and a conductivity less than 168 is classed, so far 
as sodium hazard is concerned, as an 51 water. With 
the same SAR value and a conductivity from 168 to 
2,250, it becomes an S2 water; with a conductivity 
greater than 2,250, the water is rated S3. This system 
by which waters at a constant SAR value are given a 
higher sodium-hazard rating with an increase in total 
concentrations is arbitrary and tentative, but it seems to 
be supported by field and laboratory observations. 

To use the diagram, the electrical conductivity and 
the concentrations of sodium and calcium plus mag- 
nesium for the irrigation water are required. The de- 
termination of conductivity is described in Method 72 ; 
sodium in Methods 80a and 80b; and calcium plus 
magnesium in Method 79. If only the value for calcium 
plus magnesium is known, sodium can be estimated as 
follows : 

Na + = (£CX10 6 /100) - (Ca ++ + Mg ++ ) 

Conversely, if only sodium is known, calcium plus mag- 
nesium can be estimated by the equation : 

(Ca ++ + Mg ++ ) = (ECX 107100 ) -Na + 

The ionic concentrations are expressed in milliequiva- 
lents per liter. The sodium-adsorption-ratio may be 
calculated from the equation defining the value or esti- 
mated from the nomogram of figure 22. Using the 
SAR and the EC values as coordinates, locate the cor- 
responding point on the diagram. The position of the 
point determines the quality classification of the water. 
This is illustrated by the analysis of the water of the 
Sevier River at Delta, Utah (table 12) , in which calcium 
plus magnesium equals 10.04 meq./l.; sodium, 15.31 
meq./L; and electrical conductivity, 2,400 micro- 
mhos/cm. The SAR value from the nomogram (fig. 
22) is found to be 6.8. The point on the diagram cor- 
responding to these coordinates (SAR — 6.8, ECX 10 6 — 
2,400) classifies the water as C4-S2. 

The significance and interpretation of the quality- 
class ratings on the diagram are summarized below. 

Conductivity 

Low-salinity water (CI) can be used for irriga- 
tion with most crops on most soils with little likelihood 
that soil salinity will develop. Some leaching is re- 
quired, but this occurs under normal irrigation prac- 
tices except in soils of extremely low permeability. 

Medium-salinity water (C2) can be used if a 
moderate amount of leaching occurs. Plants with 



80 



AGRICULTURE HANDBOOK 60, U. S. DEPT. OF AGRICULTURE 



100 



3 4 5 6 7 8 1000 



4 5000 



o 

QC 

< 

N 

< 

X 

Zj 

< 



Q 
O 
CO 




100 250 

CONDUCTIVITY 



750 22 50 

MICROMHOS/CM. (ECxlO 6 ) AT 25° C. 



I 



LOW 



MEDIUM 



HIGH 



VERY HIGH 



SALINITY HAZARD 



Figure 25. — Diagram for the classification of irrigation waters. 



SALINE AND ALKALI SOILS 



81 



moderate salt tolerance can be grown in most cases 
without special practices for salinity control. 

High-salinity water (C3) cannot be used on soils 
with restricted drainage. Even with adequate drain- 
age, special management for salinity control may be 
required and plants with good salt tolerance should be 
selected. 

Very high salinity water (C4) is not suitable for 
irrigation under ordinary conditions, but may be used 
occasionally under very special circumstances. The 
soils must, be permeable, drainage must be adequate, 
irrigation water must be applied in excess to provide 
considerable leaching, and very salt-tolerant crops 
should be selected. 

Sodium 

The classification of irrigation waters with respect to 
SAR is based primarily on the effect of exchangeable 
sodium on the physical condition of the soil. Sodium- 
sensitive plants may, however, suffer injury as a result 
of sodium accumulation in plant tissues when exchange- 
able sodium values are lower than those effective in 
causing deterioration of the physical condition of the 
soil. 

Low-sodium water (Si) can be used for irrigation 
on almost all soils with little danger of the development 
of harmful levels of exchangeable sodium. However, 
sodium-sensitive crops such as stone-fruit trees and avo- 
cados may accumulate injurious concentrations of 
sodium. 

Medium-sodium water (52) will present an appreci- 
able sodium hazard in fine-textured soils having high 
cation-exchange-capacity, especially under low-leach- 
ing conditions, unless gypsum is present in the soil. 
This water may be used on coarse-textured or organic 
soils with good permeability. 

High-sodium water (S3) may produce harmful 
levels of exchangeable sodium in most soils and will 
require special soil management— good drainage, high 
leaching, and organic matter additions. Gypsiferous 
soils may not develop harmful levels of exchangeable 
sodium from such waters. Chemical amendments may 
be required for replacement of exchangeable sodium, 
except that amendments may not be feasible with waters 
of very high salinity. 

Very high sodium water (S4) is generally unsatis- 
factory for irrigation purposes except at low and per- 
haps medium salinity, where the solution of calcium 
from the soil or use of gypsum or other amendments 
may make the use of these waters feasible. 

Sometimes the irrigation water may dissolve suffi- 
cient calcium from calcareous soils to decrease the 
sodium hazard appreciably, and this should be taken 
into account in the use of C1-S3 and C1-S4 waters. 
For calcareous soils with high pH values or for non- 



calcareous soils, the sodium status of waters in classes 
C1-S3, C1-S4, and C2-S4 may be improved by the 
addition of gypsum to the water. Similarly, it may 
be beneficial to add gypsum to the soil periodically 
when C2-S3 and C3-S2 waters are used. 

Effect of Boron Concentration on Quality 

Boron is essential to the normal growth of all plants, 
but the quantity required is very small. A deficiency 
of boron produces striking symptoms in many plant 
species. Boron is very toxic to certain plant species 
and the concentration that will injure these sensitive 
plants is often approximately that required for normal 
growth of very tolerant plants. For instance, lemons 
show definite and, at times, economically important 
injury when irrigated with water containing 1 p. p. m. 
of boron, while alfalfa will make maximum growth with 
1 to 2 p. p. m. of boron. 

The occurrence of boron in toxic concentrations in 
certain irrigation waters makes it necessary to consider 
this element in assessing the water quality. Scofield 
(1936) proposed the limits shown in table 14. 

Table 14,— Permissible limits of boron for several 

classes of irrigation waters 



Boron class 


Sensitive crops 


Semitolerant 
crops 


Tolerant 
crops 


1 

2 

3 

4 

5 


P. p. m. 
<0. 33 

0. 33 to . 67 
. 67 to 1. 00 

1. 00 to 1. 25 

>1.25 


P. p. m. 
<0.67 

0. 67 to 1. 33 

1. 33 to 2. 00 

2. 00 to 2. 50 

>2.50 


P. p. m. 
<1.00 

1. 00 to 2. 00 

2. 00 to 3. 00 

3. 00 to 3. 75 

>3.75 



The tolerance of crops to boron is discussed in 
chapter 4 and a boron tolerance list is given in table 
9. Boron frequently occurs in toxic concentrations 
along with the other salts that are present in saline soils. 
It can be leached from the soil but, if concentrations 
are high initially* a quantity of boron sufficient to 
cause trouble may remain after the concentration of 
other salts is reduced to a safe level. The boron status 
of saline soils should be determined as a part of a 
salinity appraisal following Method 17. 

Effect of Bicarbonate Ion Concentration on 

Quality 

On the basis of the data given in table 11 and using 
the "residual sodium carbonate" concept of Eaton 
(1950), it is concluded that waters with more than 2.5 
meq./l. "residual sodium carbonate" are not suitable 
for irrigation purposes. Waters containing 1.25 to 2.5 
meq./l. are marginal, and those containing less than 
1.25 meq./l. "residual sodium carbonate" are prob- 
ably safe. It is believed that good management prac- 



82 AGRICULTURE HANDBOOK 60, U. S. DEPT. OF AGRICULTURE 

tices and proper use of amendments might make it pos- hazards by reference to figure 25. Then considera- 

sible to use successfully some of the marginal waters tion should be given to the independent characteristics, 

for irrigation. These conclusions are based on limited boron or other toxic elements, and bicarbonate, any 

data and are, therefore, tentative. one of which may change the quality rating. Recom- 

mendations as to the use of a water of a given quality 

In appraising the quality of an irrigation water, first must take into account such factors as drainage and 

consideration should be given to salinity and alkali management practices. 



Chapter 6 



Methods for Soil Characterization 



Unless otherwise specified, all chemicals referred to 
in this chapter, as well as in chapters 7 and 8, are 
"reagent" grade and conform to standards established 
by the American Chemical Society. 

The following concentrated reagents are used. 



Reagents : 

Acetic acid 



Hydrochloric 
Nitric acid__ 
Sulfuric acid 



acid- 



Percent 

99.5 
35-38 

70 
95-96 

28 



(NH,) 





Specific 


Normality 


gravity 


18 




12 


1.19 


16 


1.42 


36 


1.84 


: 3 ) 15 


.90 



Ammonium hydroxide 

Dilutions are indicated by (1+2), ( 1+10) , and Other 

proportions. The first figure indicates the volume of 
concentrated reagent and the second the volume of 
water. 

Several methods involve centrifugation processes 
that are specified in terms of time and relative centrif- 
ugal force (RCF) , which is the ratio of the accelera- 
tion in the centrifuge to the acceleration of gravity, i. e., 
RCF= 0.00001 12XrX (r. p. m.) 2 where r. p. m. is 
centrifuge speed in revolutions per minute and r is the 
radius in centimeters from the axis of the centrifuge to 
the bottom of the centrifuge vessel when in the rotating 
position. 

Sampling, Soil Extracts, and Salinity 

Appraisal 

( 1) Soil Sample Collecting, Handling, and 
Subsampling 

A round-nose trenching spade is a convenient tool for 
sampling surface soil. A soil tube is useful for small 
subsurface samples, whereas a barrel -type auger can 
be used when larger subsurface samples are required. 
Canvas bags are generally used as containers for soil 
samples, especially for samples of 100 to 200 pounds. 
For small samples, metal boxes or cardboard cartons 
can be used. Samples for salinity measurements re- 
quire special handling, because at field-moisture con- 
tent the salt in the soil is relatively mobile and moves 
with the soil water. It has been found that kraft paper 
nail bags are satisfactory for handling samples of 
saline soil, providing the bags are first waterproofed by 
soaking in a 5 or 10 percent solution of paraffin in 
gasoline or other wax solvent. 

Soil should be air-dried before shipping or storing 
for any extended length of time. Air-dry soils that con- 



tain deliquescent salts may accumulate enough mois- 
ture during a short shipping or storage period to de- 
compose a canvas bag. A container impervious to 
water vapor should be used for such soils. Wax-treated 
bags, as mentioned above, or various types of water- 
proofed bags used for merchandising foodstuff or other 
hygroscopic material can be used. Samples in paper 
bags will withstand usual transportation handling if 
they are tightly packed in wooden boxes. To guard 
against accidental confusion of samples, it is desirable 
to place an identification tag inside the bag, in addi- 
tion to using an external marking or tag. 

The following recommendations will aid in deter- 
mining the size of sample required : 

Soil required 
Measurements to he made : * n 9 ram & 

1. Electrical conductivity of the saturation extract, 

saturation percentage, and pH of soil paste 250 

2. Soluble ion analysis (semimicro methods) for-— 

Low salinity -- -- — 500 

High salinity--- --_-- - - 250 

3. Exchangeable-cation analysis 15 

4. Hydraulic conductivity (disturbed) 400 

5. Gypsum and alkaline-earth carbonates - 50 

The total amount of soil to be obtained for the sample 
can be determined by adding up the amounts indicated 
for the individual tests to be made. If measurement 
2 is to be made, then no extra soil will be required for 
measurement 1. Samples twice as large as those indi- 
cated above are desirable, if handling facilities permit. 
Care must be taken to obtain representative sub- 
samples of a granular material such as soil. Bulk 
samples at the Laboratory are air-dried before or after 
passing through a screen with 6-mm. square openings, 
are mixed, and are stored in galvanized iron containers. 
An attempt is made to maintain a level surface of soil 
in a container so that a minimum of segregation of 
particles or aggregates occurs from rolling. A sub- 
sample of the main sample is taken by means of sev- 
eral partial loadings of a hand scoop from different 
locations on the surface of the soil. The subsample 
is then screened to the desired size. For exchangeable- 
cation analysis and other determinations requiring 
samples of about 5 gm. or less, the soil is ground to 
pass a 0.5-mm. sieve. For a number of tests relating 
to moisture retention and moisture transmission, the 
soil is passed through a 2-mm. round-hole sieve with 
the aid of a rubber stopper. One purpose of such siev- 
ing is to remove rocks larger than 2 mm.; another is to 
reduce all aggregates to less than 2 mm. In the removal 
of rocks between 2 mm. and 6 mm., they may be 

83 



84 



AGRICULTURE HANDBOOK 60, U. S. DEPT. OF AGRICULTURE 



returned to the screened sample if desired. The entire 
subsample is then placed on a mixing cloth and pulled 
in such a way as to produce mixing. Some pulling 
operations will produce segregation instead of mixing, 
and special care must be exercised to obtain a well- 
mixed sample. The soil sample is then flattened until 
the pile is 2 to 4cm. deep. 

For moisture retentivity, hydraulic conductivity, and 
modulus of rupture tests, 2 to 6 subsamples, each hav- 
ing a fairly definite volume, are required. Use paper 
cups to hold the individual subsamples. Mark with 
a pencil line around the inside of the cup the height to 
which the cup is to be filled to give the correct amount 
of subsample. Then, using a thin teaspoon or a small 
scoop, lift small amounts of soil from the pile, placing 
each in successive cups and progressing around the pile 
until the cups are filled to the desired level. It is diffi- 
cult with some soils, especially if they have been passed 
through a 2-mm. round-hole sieve, to take samples from 
the pile without allowing the larger particles to roll off 
the spoon or scoop. This rollback should be avoided 
because it makes the extracted subsample nonrepre- 
sentative. The rollback problem is practically absent 
from some soils, especially if all the sample has been 
passed through an 0.5-mm. sieve. 

Three data forms, or work sheets, used at the Labora- 
tory are shown herewith. The field data sheet should 
be at hand during sampling as an aid in recording 
pertinent information. The other two forms serve as 
work sheets for recording and calculating laboratory 
determinations. 

(2) Saturated Soil Paste 

Apparatus 

Container of 250-ml. capacity or greater, such as a 
cup or moisture box. 

Procedure 

Prepare the saturated soil paste by adding distilled 
water to a sample of soil while stirring with a spatula. 
The soil-water mixture is consolidated from time to 
time during the stirring process by tapping the con- 
tainer on the workbench. At saturation the soil paste 
glistens as it reflects light, flows slightly when the con- 
tainer is tipped, and the paste slides freely and cleanly 
off the spatula for all soils but those with a high clay 
content. After mixing, the sample should be allowed 
to stand for an hour or more, and then the criteria for 
saturation should be rechecked. Free water should not 
collect on the soil surface nor should the paste stiffen 
markedly or lose its glistening appearance on standing. 
If the paste does stiffen or lose its glisten, remix with 
more water. 

Because soils puddle most readily when worked at 
moisture contents near field capacity, sufficient water 
should be added immediately to bring the sample nearly 
to saturation. If the paste is too wet, additional dry 
soil may be added. 



The amount of soil required depends on the measure- 
ments to be made, i. e., on the volume of extract de- 
sired. A 250-gm. sample is convenient to handle and 
provides sufficient extract for most purposes. I nitially, 
the sample can be air-dry or at the field -moisture con- 
tent, but the mixing process is generally easier if the soil 
is first air-dried and passed through a 2-mm. sieve. 

If saturation pastes are to be made from a group of 
samples of uniform texture, considerable time can be 
saved by carefully determining the saturation percent- 
age of a representative sample i n the usual way. Subse- 
quent samples can be brought to saturation by adding 
appropriate volumes of water to known weights of soil. 

Special precautions must be taken with peat and 
muck soils and with soils of very fine and very coarse 
texture. 

Peat and muck soils. — Dry peat and muck soils, 
especially if coarse or woody in texture, require an 
overnight wetting period to obtain a definite endpoint 
for the saturated paste. After the first wetting, pastes 
of these soils usually stiffen and lose the glisten on 
standing. Adding water and remixing then gives a mix- 
ture that usually retains the characteristics of a satu- 
rated paste. 

Fine-textured so il s. -To minimize puddling and 
thus obtain a more definite endpoint with fine-textured 
soils, the water should be added to the soils with a mini- 
mum of stirring, especially in the earlier stages of 
wetting. 

Coarse -textured soils. — The saturated paste for 
coarse-textured soils can be prepared in the same man- 
ner as for fine-textured soils; however, a different mois- 
ture content is recommended for the salinity appraisal 
of such soils (Method 3b). 

Method 27 gives procedures for determining the 
moisture content of saturated paste, i. e., the saturation 
percentage. 

(3) Soil -Water Extracts 
(3a) Saturation Extract 

Apparatus 

Richards or Buechner funnels, filter rack or flask, 
filter paper, vacuum pump, extract containers such as 
test tubes or 1-oz. bottles. 

Procedure 

Transfer the saturated soil paste, Method 2, to the 
filter funnel with a filter paper in place and apply 
vacuum. Collect the extract in a bottle or test tube. 
Pyrex should not be used if boron is to be determined. 
If the initial filtrate is turbid, it can be refiltered 
through the soil or discarded. Vacuum extraction 
should be terminated when air begins to pass through 
the filter. If carbonate and bicarbonate determinations 
are to be made on the extract, a solution containing 
1,000 p. p. m. of sodium hexametaphosphate should be 
added at the rate of one drop per 25 ml. of extract prior 



SALINE AND ALKALI SOILS 



85 



Soil Ace. No. 
Temporary No. 



Sampled by 



State 



Site location & 
Station or farm 



UNITED STATES SALINITY LABORATORY 
FIELD DATA FOR SOIL SAMPLES 



Mail address 



County 



Nearest 
settlement 



M, Sec. - 



.; R 



Date 



District or valley 



Directions for finding site: (Use reverse side for a sketch of roads showing nearest settlement and distance from local landmarks.) 



References (Soil Survey Bui., other publications, or correspondence): 



Profile description (color, texture, structure, horizons, hardpan, origin, parent material, water table, drainage, and soil series if 
known) : 



Topography 



Surface si ope. 



Percent topsoi I erosion 



Microrelief at the sampling site, furrow, ridge, etc. 



Disturbance from land preparation, leveling, filling, etc. 



Sample: D£ji±Ji N o . sa_c_k_s Approx. total wt. (lb.) 

Composite sample: Depth No. h o I es Sampling method and pattern 



Approx. total wt. (lb.) 



Undisturbed structure sample: Depth No. of replicates 

Yrs. of cultivation Yrs. of i r r i gallon Source of water 

Crop data (rotation, yield history, detailed description of plant condition at time of sampling): 



Management practices: 



(It is expected that not all the above blanks can be filled for every sample but the usefulness of laboratory determinations depenc!6 
on the completeness and accuracy of the field data.) 



86 



AGRICULTURE HANDBOOK 60, U. S. DEPT. OF AGRICULTURE 



Soil sample No . 



. Description: 



Moisture in air-dry Soil 



Can No. 



Air-dry Oven-dry 



Gross 



Tare 
Net 

OD 



AD 



w 



Saturation Percentage 



From Water Added 



'an No. 



Air-dry soil, gm#- 
Oven-dry soil, gm< 
H20,hlU( 

+ ) 



Vj at sat • P w at sat • 



(Oven-dry basis) 1 (Oven- dr y (Oven-dry basis) 



By Drying 



Can No. 



Wet 



Oven-dry 



Gross 

Tare 

Net 



basis) 



pH of Saturated Soil Paste 



Electrical Conductivity 



Alkaline-earth Carbonates 



Saturation Extract 



T°C 



( Lime) 
(Scale: low, medi um^ high) 



pH of Saturation Extract 



Lime 




R 



Boron 



ml . 



pH of Suspension 

Soil 

Water 



?5r , p»p«3u_ 



B 



Millimhos/cm# 

at 25° C. 



B 
p*p«m« 



Calcium plus Magnesium 
(Versenate titration) 



Sodium 



Potassium 



Standard 



r ■- 



meq»/l • 
- meq»/l» 



Standard 



meq # /l« 
meq./l* 



Ca+Mg, sat. ext . 
meq •/!• 

Ca+Mg, dry soil 
meq»/lOO gnu 



Na, sat. ext. 
meq»/l. 

Na f dry soil 
ioeq # /lOO gm« 



K, sat. ext. 
meq #/l • 

K» dry soil 
meq»/lOO gm, 




SALINE AND ALKALI SOILS 



87 



Soil Sample No. 


1 


Centrifuge tube number 








2 


Sample, air-dry weight gnu 








3 


Sample , oven-dry weight gnu 










CATION- EXCHANGE -CAPACITY 










(Saturated with NaAc: Na by flame photometer) 








4 


Extracting solution, "diluted to mi# 








5 


Dilution: Solution 4 dilution ratio 








6 


Flame photometer standard Na meq./l # 








7 


Flame photometer reading 








8 


Sodium, from graph meq./l # 








9 


Cation-exchange-capacity (0D basis) meq#/100 5. 










EXCHANGEABLE SODIUM 








10 


Extracting solution (NH^Ac) diluted to ml. 








11 


Dilution: Solution 10 dilution ratio 








12 


Flame photometer standard Na meq»/l« 








13 


Flame photometer reading 








14 


Sodium, from graph meq«/li 








15 


Total sodium (OD basis) meq # /lOO gm. 








16 


Sodium in sat» extract (OD basis) meq«/lOO gm # 








17 


Exchangeable sodium (OD basis) meq./lOO gnu 








18 


Exchangeable -s od ium-pe rcent age 










EXCHANGEABLE POTASSIUM 








19 


Extracting solution (N^Ac) diluted to ml# 








20 


Dilution: Solution 19 dilution ratio 








21 


Flame photometer standard K meqt/l« 








22 


Flame photometer reading 








23 


Potassium, from graph meq # l t 








24 


Total potassium (OD basis) meq«/100 gm« 








25 


Potassium in sat. extract (OD basis) meq./lOO gm* 








26 


Exchangeable potassium (OD basis) meq#/100 gm ( 








27 


Exchangeable-potassium-percentage 









88 



AGRICULTURE HANDBOOK 60, U. S. DEPT. OF AGRICULTURE 



to stoppering and storing. This prevents the precipita- 
tion of calcium carbonate on standing. 

For appraising soil salinity for most purposes, the 
extraction can be made a few minutes after preparing 
the saturated paste. If the soil contains gypsum, the 
conductivity of the saturation extract can increase as 
much as 1 or 2 mmhos/cm, upon standing. There- 
fore, if gypsum is present, allow the saturated paste to 
stand several hours before extracting the solution. 

If the solution is to be analyzed for its chemical 
constituents, the saturated paste should stand 4 to 16 
hours before extraction. 



Richards (1949a), Reitemeier and Fireman (1944). 

(3b) Twice-Saturation Extract for Coarse- 
Textured Soils (Tentative) 

The following procedure gives a moisture content 
that is approximately 8 times the 15-atmosphere per- 
centage instead of 4 times, which is a usual factor for 
the saturation percentage of finer textured soils. The 
conductivity of the "tw ice-saturation" extract, there- 
fore, is doubled before using the standard saturation- 
extract scale for salinity evaluation. 

Apparatus 

Soil container of 10 to 12 cm. diam. (i. e., I -lb. cof- 
fee can) with a loosely fitting basket formed from 
galvanized screen with openings approximately 6 mm. 
square. 

Pipet,2-mL capacity. Other items are the same as 
for M ethod 3a. 

Procedure 

Place the wire basket in the can, fill the basket with 
soil to a depth of 2 or 3 cm. Level the soil and by use 
of a pipet add 2 ml . of water dropwise to noncontiguous 
spots on the soil surface, cover, and allow to stand for 
15min. Gently sift the dry soil through the wire basket 
and weigh the moist pellets of soil retained thereon. 
Calculate the moisture content of the pellets as follows: 

P w = (2Xl00)/(wet weight in grams-2) 

Weigh 250 gm. of air-dry soil and add sufficient water 
to make the moisture content up to 4 times the value 
found in the pellets. Use a vacuum filter to obtain the 
soil extract. For salinity appraisal of coarse-textured 
soil from which this extract was obtained, determine the 
electrical conductivity of the extract at 25° C. Multi. 
ply this conductivity value by 2 before using the stand- 
ard saturation-extract salinity scale for interpretation 
(chs. 2 and 4). 

(3c) Soil-Water Extracts at 1:1 and 1: 5 

Apparatus 

Filter funnels, fluted filter paper, and bottles for soil 
suspensions and filtrates. 



Procedure 

Place a soil sample of convenient size in a bottle, add 
the required amount of distilled water, stopper, and 
agitate in a mechanical shaker for 15 min. Allow the 
contents to stand at least an hour, agitate again for 
5 min., and filter. If shaken by hand, invert and shake 
bottle vigorously for 30 sec. at least 4 times at 30-min. 
intervals before filtering. 

At a 1: 1 soil-water ratio, it may be desirable to cor- 
rect for hygroscopic moisture. Unless high precision 
is required, this is done by grouping the air-dried and 
screened soils roughly according to texture, and deter- 
mining the percent moisture in 2 or 3 samples from each 
textural group. It is then possible to weigh out soil 
samples from the various groups and add sufficient 
water to bring the samples to approximately 100 per- 
cent moisture by weight. For example, an air-dry soil 
containing 3 percent moisture on an oven-dry basis can 
be brought to a 1: 1 soil-water ratio by adding 97 ml. 
water to 103 gm. of air-dried soil. 

At a soil-water ratio of 1: 5 or greater, no allowance 
is ordinarily made for moisture in the air-dried sample. 

(3d) Soil Extract in the Field-Moisture 
Range 

A displacement method such as used by White and 
Ross (1937) does not require complicated apparatus; 
however, the pressure-membrane method described 
here can be used for a wider range of soil textures and 
a wider range of moisture contents. 

Apparatus 

Pressure-membrane cell with a cylinder 5 or 10 cm. 
high, tank of commercial water-pumped nitrogen, cans 
with watertight lids, plain transparent cellophane No. 
600. 

Procedure 

Prior to use, the sheets of No. 600 cellophane are 
soaked in distilled water with daily changes of water in 
order to reduce the electrolyte content of the membrane. 
Electrical conductivity measurements on the water will 
indicate when the bulk of these impurities has been re- 
moved. Since washed and dried membranes may be 
somewhat brittle, they are stored wet until ready for 
use. They should be partially dried before mounting in 
the pressure-membrane apparatus, 

The soil should be brought from the field at the 
moisture condition desired for the extraction and im- 
mediately packed in the pressure-membrane apparatus. 
If the soil has been air-dried, it may be passed through 
a6-mm. screen and wetted to the desired water content 
with a fine spray of distilled water while tumbling in a 
mixing can or on a waterproofed mixing cloth. This 
wetted soil is stored in an airtight container, preferably 
in a constant-temperature room for 2 weeks and is 
mixed occasionally during this time. The pressure- 
membrane apparatus is then assembled, using No. 600 



SALINE AND ALKALI SOILS 



89 



plain transparent cellophane for the membrane. The 
soil is firmly packed by hand on the membrane in the 
extraction chamber to a depth of 2 or 4 in., depending 
upon the height of cylinder available. The chamber is 
then closed and the extraction process started at 225 
lb. per sq. in. (15 atm.) of nitrogen gas. 

The extract should be collected in fractions of ap 
proximately equal volume. The first fraction is usually 
discarded to avoid contamination from the membrane. 
Electrical conductivity measurements can be made on 
subsequent fractions to determine the degree of uni- 
formity of the extract. The extraction process may 
require 1 to 4 days. 



Reitemeier (1946) , Reitemeier and Richards (1944), 
Richards (1947), and White and Ross (1937). 

(4) Electrical Conductivity of Solutions 

(Pa) Standard Wheatstone Bridge 

Remarks 

Electrical conductivity is commonly used for indicat- 
ing the total concentration of the ionized constituents 
of solutions. It is closely related to the sum of the 
cations (or anions) as determined chemically and 
usually correlates closely with the total dissolved solids. 
It is a rapid and reasonably precise determination that 
does not alter or consume any of the sample. 

Apparatus 

Wheatstone bridge, alternating current, suitable for 
conductivity measurements. This may be a 1,000-cycle 
a. c. bridge with telephone receivers, a 60-cycle a. c. 
bridge with an a. c. galvanometer, or one of the newer 
bridges employing a cathode ray tube as the null 
indicator. 

Conductivity cell, either pipet or immersion type, 
with platinized platinum electrodes. The cell constant 
shoufd be approximately 1.0 reciprocal centimeter. 
New cells should be cleaned with chromic-sulfuric acid 
cleaning solution, and the electrodes platinized before 
use. Subsequently, they should be cleaned and replat- 
inized whenever the readings become erratic or when an 
inspection shows that any of the platinum black has 
flaked off. The platinizing solution contains platinum 
chloride, 1 gm., lead acetate, 0.012 gm., in 100 ml. 
water. To platinize, immerse the electrodes in the 
above solution and pass a current from a 1.5.volt dry 
battery through the cell. The current should be such 
that only a small quantity of gas is evolved, and the di- 
rection of current flow should be reversed occasionally. 

A thermostat is required for precise measurements, 
but for many purposes it is satisfactory to measure the 
temperature of the solution and make appropriate 
temperature corrections. 



Potassium chloride solution, 0.01 N . Dissolve 0.7456 
gm. of dry potassium chloride in water and make to 1 
liter at 25" C. This is the standard reference solution 
and at 25" C. has an electrical conductivity of 1411.8 
X 10- 6 (0.0014118) mhos/cm. 

Procedure 

Fill the conductivity cell with the reagent, having 
known conductivity EC 25 . Most cells c&y a mark 
indicating the level to which they should be filled or 
immersed. Follow the manufacturers' instructions in 
balancing the bridge. Read the cell resistance, R 25 at 
25" C. and calculate the cell constant (A), from the 
relation, 

k= EC,, X/? 25 

The cell constant will change if the platinization fails, 
but it is determined mainly by the geometry of the 
cell, and so is substantially independent of temperature. 
Rinse the cell with the solution to be measured. The 
adequacy of rinsing is indicated by the absence of 
resistance change with successive rinsings. If only a 
small amount of the sample is available, the cell may 
be rinsed with acetone and ventilated until it is dry. 
Record the resistance of the cell (R t ) and the temper- 
ature of the solution ( t ) at which the bridge is bal- 
anced. Keep the cell filled with distilled water when 
not in use. 

Calculations 

The electrical conductivity (EC,) of the solution at 
the temperature of measurement ( t ) is calculated from 
the relation 

EC, = k/R, 
where 

k = EC„xR 25 

For soil extracts and solutions, a temperature con- 
version factor (ft), obtained from table 15, can be 
used for converting conductivity values to 25" C. Thus, 

EC 25 =EC t Xf t =kf t /R t 



Campbell and others (1948), National Research 
Council International Critical Tables (1929). 

(4b) Direct Indicating Bridge 

Apparatus 

Conductivity sets are available that have a bridge 
scale and cell design features suggested by the Labora- 
tory especially for use with saturation extracts (fig. 26) . 
This set is convenient to use and has sufficient accuracy 
for diagnostic purposes. The conductivity cell sup- 
plied with this bridge has a constant of 0.5 cm." 1 and a 
capacity of 2 to 3 ml. of solution. With this cell the 



259525 O - 54 - 7 



90 



AGRICULTURE HANDBOOK 60, U. S. DEPT. OF AGRICULTURE 



Table 15.- 



Temperature factors (/*) for correcting resistance and conductivity data on soil extracts to the 

standard temperature of 25° C. 

EC 25 =EC t X ft; EC 25 ~(k/R t ) X ft; R 2 5=RJft 



°c. 


°F. 


ft 


°C. 


°F. 


/* 


°C. 


F. 


ft 


3.0 


37.4 


1.709 


22.0 


71.6 


1.064 


29.0 


84.2 


0.925 


4.0 


39.2 


1.660 


22.2 


72.0 


1.060 


29.2 


84.6 


.921 


5.0 


41.0 


1.613 


22.4 


72.3 


1.055 


29.4 


84.9 


.918 


6.0 


42.8 


1.569 


22.6 


72.7 


1.051 


29.6 


85.3 


.914 


7:o 


44.6 


1.528 


22.8 


73.0 


1.047 


29.8 


85.6 


.911 


8.0 


46.4 


1.488 


23.0 


73.4 


1.043 


30.0 


86.0 


.907 


9.0 


48.2 


1.448 


23.2 


73.8 


1.038 


30.2 


86.4 


.904 


10: 


50.0 


1.411 


23.4 


74. 1 


1.034 


30.4 


86.7 


.901 


11.0 


51.8 


1.375 


23.6 


74. 5 


1.029 


30.6 


87. 1 


.897 


12.0 


53.6 


1.341 


23.8 


74.8 


1.025 


30.8 


87.4 


.894 


13. 


55.4 


1.309 


24.0 


75. 2 


1.020 


31.0 


87.8 


.890 


14.0 


57.2 


2.277 


24.2 


75.6 


1.016 


31.2 


88.2 


,887 


15.0 


59.0 


1.247 


24.4 


75.9 


1.012 


31.4 


88.5 


.884 


16.0 


60.8 


J. 218 


24.6 


76.3 


1.008 


31.6 


88.9 


.880 


17. 


62.6 


1. 189 


24.8 


76.6 


1.004 


31.8 


89.2 


.877 


18. 


64.4 


1.163 


25.0 


77.0 


1.000 


32.0 


89.6 


.873 


18. 2 


64.8 


1.157 


25.2 


77.4 


.996 


32.2 


90.0 


.870 


18.4 


65. 1 


1.152 


25.4 


77.7 


.992 


32.4 


90.3 


.867 


18.6 


65.5 


1.147 


25.6 


78. 1 


.988 


32.6 


90.7 


.864 


18. 8 


65.8 


1.142 


25.8 


78. 5 


.983 


32.8 


91.0 


.861 


19.0 


66.2 


1.136 


26.0 


78.8 


.979 


33.0 


91.4 


,858 


19.2 


66.6 


1.131 


26.2 


79. 2 


.975 


34.0 


93.2 


.843 


19.4 


66.9 


1.127 


26.4 


79.5 


.971 


35.0 


95.0 


,829 


19.6 


67.3 


1.122 


26.6 


79.9 


.967 


36.0 


96.8 


.815 


19.8 


67.6 


1.117 


26.8 


80.2 


.964 


37.0 


98.6 


.801 


20.0 


68.0 


1.112 


27.0 


80.6 


.960 


38.0 


100.2 


788 


20.2 


68.4 


1.107 


27.2 


81.0 


.956 


39.0 


102.2 


:775 


20.4 


68.7 


1.102 


27.4 


81.3 


.953 


40.0 


104.0 


.763 


20.6 


69.1 


1.097 


27.6 


81.7 


.950 


41.0 


105.8 


750 


20.8 


69.4 


1.092 


27.8 


82.0 


.947 


42.0 


107.6 


:739 


21.0 


69.8 


1.087 


28.0 


82.4 


.943 


43.0 


109.4 


.727 


21.2 


70.2 


1.082 


28.2 


82.8 


.940 


44.0 


111.2 


.716 


21.4 


70.5 


1.078 


28.4 


83. 1 


.936 


45.0 


113.0 


.705 


21.6 


70.9 


1.073 


28.6 


83.5 


.932 


46.0 


114.8 


.694 


21.8 


71. 2 


1.068 


28.8 


83.8 


.929 


47.0 


116.6 


.683 



bridge scale reads directly from 0.15 to 15 mmhos/cm. 
The bridge is operated by alternating current and makes 
use of a cathode ray tube null indicator. When the 
temperature of the solution is set on the temperature- 
compensating dial, the main dial, at balance, indicates 
electrical conductivity at 25" C. 

The accuracy of calibration of the bridge scale should 
be checked with a saturated solution of calcium sulfate 
di hydrate. With the temperature-compensation dial 
correctly set, the bridge should read 2.2 mmhos/cm. 
with this solution. 

Procedure 

Obtain the saturation extract in accordance with 
M ethod 3a. Read the temperature of the extract. Rinse 
and fill the conductivity cell. Set the temperature com- 



pensation dial. Close the contact switch on the cell 
briefly while balancing the bridge with the main dial. 
Read and record the electrical conductivity in milli- 
mhos per centimeter at 25" C. 

If the bridge will not balance, the conductivity of the 
extract may be below 0.15 or above 15 mmhos/cm. If 
above, estimate conductivity by adding 9 parts of dis- 
tilled water to 1 part of extract, by volume, and balanc- 
ing the bridge with the diluted extract in the cell. The 
conductivity of the undiluted extract will be approxi- 
mately 10 times the conductivity reading obtained on 
the diluted extract. 

Alternatively, for concentrated extracts, a cell with a 
constant higher than 0.5 may be used. If, for example, 
the value of the cell constant is 5.0, then the scale read- 
ing of the bridge must be multiplied by 10. 



SALINE AND ALKALI SOILS 



91 



























'^ %^A^^d 






Ififfll 






Figure 26. — Bridge and cell for treasuring the conductivity of saturation extracts and irrigation waters 



(5) Resistance of Soil Paste and Percent 
Salt in Soil 

Apparatus 

Bureau of Soils electrode cup, alternating current 
Wheatstone bridge, and thermometer. 

Procedure 

Fill the electrode cup with saturated soil paste pre- 
pared in accordance with Method 2. Tap the soil cup 
on the workbench to remove air bubbles and strike off 
the soil paste level with the upper surface of the cup. 
M easure the resistance and the temperature of the soil 
paste i n the cup. U se tabl e 16 to convert the resi stance 
reading to the temperature of 60" F. Then, by means 
of table 17, convert the paste resistance at 60" to ap- 
proximate percent salt. Inasmuch as the saturation per- 
centage varies with soil texture, it is necessary to esti- 
mate the textural class of the sample and to select the 
appropriate column in the table for making the con- 
version from resistance to percent salt. 



References 

Davis and Bryan (1910), Soil Survey Manual 
(1951). 

(6) Freezing-Point Depression 

(6a) Freezing-Point Depression of Solu- 
tions 

Apparatus 

Wheatstone bridge with approximately the following 
characteristics: 1,000 ohms equal arm ratio, 10,000- 
ohm decade balancing resistance adjustable to 1 ohm; 
galvanometer : type E, Leeds and N orthrup D M -2430-c, 
or equivalent. Use a 2-volt lead cell for the bridge 
voltage supply. Thermistor: type 14B, Western Elec- 
tric. Freezing bath: with either refrigerating coil or 
salt-ice mixture. Freezing tube: test tube 1.5 cm. in- 
side diameter X 15 cm. long with rubber stopper. Air- 
jacket: test tube 2.9 cm. outside diameter X 20 cm. 
long. Use cork bushings cut by means of a grinding 



92 



AGRICULTURE HANDBOOK 60, U. S. DEPT. OF AGRICULTURE 



Table 16. — Bureau of Soils data for reducing soil paste resistance readings to values at 60° F. (Whitney and 

Means, 1897)' 



40 

42 

44:::::::::::: 

46 

48 

50 

52 

54 

56 

58 

60 

62 

64 

66 

68 

70 

72 

74 

76 

78 

80 

82 

84 

86 

d d i i i i i i i i i i i i i 

90 

92 

94 

96 

98 



Ohms 



1,000 



735 
763 
788 
814 

a43 

867 
a93 
917 
947 
974 

1,000 
1,027 
1,054 
1,081 
1,110 

1,140 
1,170 
1,201 
1,230 
1,261 

1,294 
1,327 
1,359 
1,393 
1,427 

1,460 
1,495 
1,532 
1,570 
1,611 



2,000 



1,470 
1,526 
1,576 
1,628 
1,686 

1,734 
1,786 
1, a34 

1, a94 
1,948 

2,000 
2,054 
2,108 
2,162 
2,220 

2,280 
2,340 

2, 402 
2,460 
2,522 

2,598 
2,654 
2,718 
2,786 
2, a54 

2,920 
2,990 
3,064 
3,140 
3,222 



3,000 



2,205 
2,289 
2,364 
2,442 
2,529 

2,601 
2,679 
2,751 
2, a41 
2,922 

3,000 
3,081 
3,162 
3,243 
3,330 

3,420 
3.510 
3,603 
3,690 
3,783 

3,882 

3,981 
4,077 
4,179 
4,281 

4,380 
4,485 
4,596 
4,710 

4, a33 



4,000 



2,940 
3,052 
3,152 
3,256 
3,372 

3,468 
3,572 
3,668 
3,780 
3,896 

4,000 
4,108 
4,216 
4,324 
4,440 

4,560 
4,680 
4,804 

4,920 
5,044 

5,176 
5,308 
5,436 
5,572 
5,708 

5, a40 
5,980 
6,128 
6,280 
6,444 



5,000 



3,675 
3,815 

3,940 
4,070 
4,215 

4,335 
4,465 
4,585 
4,735 
4, a70 

5,000 
5,135 
5,270 
5,405 
5,550 

5,700 
5,850 
6,005 
6,150 
6,305 

6,470 
6,635 
6,795 
6,965 
7,135 

7,300 
7,475 
7,660 
7,850 
a, 055 



6,000 



4,410 
4,578 
4,728 
4,884 
5,058 

5,202 
5,358 
5,502 
5,682 

5, a44 

6,000 
6,162 
6,324 
6,486 
6,660 

6, a40 
7,020 
7,206 
7,380 
7,566 

7,764 
7,962 
a, 154 

a, 358 
a, 562 

a, 760 
a, 970 
9,192 
9,420 
9,666 



7,000 



5,145 
5,341 
5,516 
5,698 
5,901 

6,069 
6,251 
6,419 
6,629 
6, ala 

7,000 
7,189 

7,378 
7,567 
7,770 

7,980 
a, 190 
a, 407 
a, 610 
a, a27 

9,058 
9,289 
9,513 
9,751 
9,989 

10,220 
10,465 
10,724 
10,990 
11,277 



a, 000 



5,880 
6,104 
6,304 
6,512 
6,744 

6,936 
7,114 
7,336 
7,576 
7,792 

a, 000 
a, 216 
a, 432 
a, 648 
a, 880 

9,120 
9,360 
9,608 
9, a40 
lo, 088 

10,352 
10,616 
lo, a72 
11,144 
11,416 

11,680 
11,960 
12,256 
12,560 
12,888 



9,000 



6,615 
6, a67 
7,092 
7,326 
7,587 

7,803 
a, 037 
a, 253 
a, 523 
a, 766 

9,000 
9,243 
9,486 
9,729 
9,990 

10,260 
10,530 
lo, 809 
11,070 
11,349 

11,646 
11,943 
12,231 
12,537 
12, a43 

13,140 
13,455 
13,788 
14,130 
14,499 



1 Example: Suppose the observed resistance is 2,568 ohms at 50° F. In the table at that temperature, we find that 2,000 
ohms is equal to 1,734 ohms at 60° F ., 5,000 ohms is equal to 4,335 ohms at 60° F ., hence 500 ohms would he equal to 434 ohms. 
Similarly, 60 ohms would he one-hundredth of 6,000 ohms in the table and therefore equal to approximately 52 ohms at 60° F., 
while a ohms would he equal to about 7 ohms. These separate values are added together thus, 

2,000 1,734 

500 434 

60 52 

a 7 



2,568 ohms at 50°=2, 227 ohms at 60° 



machine to center and suspend the freezing tubes in 
the air-jackets. M ount the thermistor on a glass tube 
with plastic spacers so as to hold the thermosensitive 
bead at the center of a 5-ml. sample of the solution to 
be frozen. Plot a resistance-temperature calibration 
curve for the thermistor over the range from 1 to — 5" 
C, using a standard thermometer or other source of 
reference temperature. 

Procedure 

Place S-ml. samples of solutions in the freezing tubes 
and mount the tubes in the air-jacket in the freezing 
bath. An undercooling of approximately 2" C. has 
been found convenient for soil extracts and plant saps. 



Place the thermistor in one of the samples when the 
sample has attained the bath temperature as indicated 
by the bridge resistance reading. Induce freezing by 
touching the solution with a metal probe cooled with 
solid carbon dioxide. Follow the course of the freez- 
ing by keeping the bridge approximately balanced un- 
til the minimum resistance (maximum temperature) 
is attained. With an undercooling of 2" O, a time of 
about 2 min. is required to attain the maximum ob- 
served freezing temperature. The minimum resistance 
value is recorded as the freezing resistance. The ther- 
mistor can then be transferred rapidly to the next 
sample so that ice crystals carried over in the process 
may initiate freezing. Include a tube of distilled 



SALINE AND ALKALI SOILS 



93 



Table 17. — Bureau of Soils data for relating the 
resistance of soil paste at 60° F. to percentage of 
"mixed neutral salts" in soil (Davis and Bryan, 
1910) 



Resistance 


Salts in — 


at 60" F. 
(ohms) 


Sand 


Loam 


Clay loam 


Clay 




Percent 
3.00 
2.40 
2.20 
1.50 
1.24 
1.04 

.86 
.75 
.67 
.60 
.55 
.51 

.48 
.45 
.42 
.39 
.37 
.35 

.33 
.31 
.30 
.28 

.27 
.25 

.24 
.23 
.22 
.21 
.21 
.20 

.20 
.19 
.19 


Percent 
3.00 
2.64 
2.42 
1. 70 
1.34 
1. 14 

.94 
.78 
.71 
.64 
.58 
.54 

.50 
.47 
.44 
.42 
.39 
.37 

.35 
.33 
.32 
.29 
.28 
.26 

.25 
.24 
.23 
.22 
.21 
.21 

.20 
.20 
. 19 


Percent 


Percent 


if:::::::::: 

20 


3.00 
2.80 
1.94 
1.46 
1.22 

1.04 
.88 

.77 
.69 
.63 
.57 

.53 
.50 

.47 
.44 
.41 
.39 

.37 
.35 
.33 
.31 
.29 
.28 

.26 
.25 
.24 
.23 
.22 
.21 

.21 
.20 
.20 


3.00 


25 
30:::::::::: 

35 


2.20 
1.58 
1.32 


40 

45 


1.14 
.98 


50 

55 


.86 

.77 


60 


.70 


65 


.63 


70 

75 

80 


.59 
.55 
.51 


85 

90 


.48 

. 45 


95 


.42 


100 


.39 


105 

110 


.37 
.35 


115 


.33 


120 


.32 


125 

130 


.30 
.28 


135 

140 

145 

150 

155 

160 

165 


.27 
.26 
.25 
.24 
.23 

.22 
.21 


170 


.20 



where OP is the osmotic pressure in atmospheres and 
AT is the freezing-point depression in degrees centi- 
grade. Harris and Gortner (1914) present a table 
of osmotic pressures in atmospheres covering the range 
of to 2.999" C. freezing-point depression. 



water with each batch of samples to provide a check on 
the resistance thermometer. 

Calculations 

By means of the standard curve constructed for the 
particular thermistor in use, convert the freezing re- 
sistance to degrees centigrade. Correct for under- 
cooling, using the following relationship: 

AT- AT, (1-0.0125^) 

where AT is the corrected freezing-point depression, 
AT, is the observed freezing-point depression, and u 
is the undercooling in degrees centigrade. A table 
of factors for correction for undercooling is given by 
Harris (1925). Calculate osmotic pressure from the 
equation : 

OP = 12.06 A T- 0.021 A T 2 



Richards and Campbell (1948, 1949). 

(6b) Freezing-Point Depression of Water 
in Soil Cores 

Apparatus 

Use the same resistance thermometer as in Method 
6a, except the thermistor must be enclosed in a thin- 
walled metal tube sealed at the lower end and fastened 
at the upper end to the glass mounting tube. The 
calibration curve should be plotted for this thermistor 
after mounting in the protective metal jacket. 

Soil sampling tube to deliver soil cores 1.7 cm. in 
diameter. Freezing tubes-glass test tube 2.0 cm. in- 
side diameter (2.2 cm. outside diameter) X 17.0 cm. 
long with rubber stoppers. Soil core holders of rigid 
tubular material (hard rubber), 1.7 cm. inside diam. 
(1.9 cm. outside diameter) x 5.1 cm. long. Covers 
for soil core holders are disks of hard plastic material 
(Lucite), 1.9 cm. diam. x3 mm. thick. One-half of 
the peripheral surface is turned to a smaller diameter 
(approximately 1.7 cm.) to give a snug fit in the ends 
of the soil core holders. A tapered hole large enough 
to accommodate the jacketed thermistor is drilled in 
one-half of the covers just described. 

The Wheatstone bridge, galvanometer, freezing 
bath, and air-jacket tubes are as described in Method 
6a. It is convenient to construct wooden racks to hold 
about 30 freezing tubes each. 

Procedure 

Soil cores are pushed from the sampling tube into 
the soil core holders and cut to length. A solid disk 
cover is placed on the bottom and a disk with a hole 
is placed on the top of the soil core holder. The disks 
are then pressed into position and are held there by the 
shoulder machined for that purpose. The cores are 
placed in the freezing tubes that are closed with rub- 
ber stoppers bearing the sample numbers. If the sam- 
ples are to be stored for some time before freezing, 
both ends of the core holder may be dipped into melted 
paraffin to prevent moisture loss. 

Prior to freezing the sample, a hole is drilled in the 
center of the soil core. The diameter of this hole 
should be slightly smaller than the thermistor jacket. 
The disturbance caused by insertion of the thermistor 
in an undercooled sample will then initiate freezing. 
The hole is drilled by hand with a twist drill mounted 
in a plastic rod having a free fit in the freezing tube. 

The freezing tubes containing the samples to be 
frozen are centered and suspended in the air-jacket 



94 



AGRICULTURE HANDBOOK 60, U. S. DEPT. OF AGRICULTURE 



tubes by means of a cork bushing. The thermistor is 
inserted into a soil core when the freezing bath is 
initially loaded so that the approach of the tempera- 
ture of the cores to the bath temperature can be fol- 
lowed. The bath temperature should be held constant 
±0.1° C. at approximately 1.5" below the expected 
freezing points for the batch of cores. When the 
samples attain the bath temperature, freezing of the 
first core is induced by a twist of the thermistor. Suc- 
ceeding samples usually start to freeze at the time the 
thermistor is inserted into the sample. Frozen 
samples can be replaced in the bath with unfrozen 
samples, so that for a bath with capacity for 30 samples 
there is no waiting for undercooling of samples after 
the initial batch. An interval of about 1 hour is 
usually sufficient for samples at room temperature to 
come to bath temperature. 

As with the solutions, the change in resistance (tem- 
perature) is followed by means of the galvanometer, 
and the minimum resistance (maximum temperature) 
recorded as the freezing resistance. 

Calculations 

The freezing resistance is converted to observed 
freezing-point depression in degrees centigrade by 
means of the calibration curve of the thermistor. N o 
convenient method seems to be available at present for 
making an undercooling correction for water in soil. 
There is experimental indication that the undercooling 
correction is small for undercooling of 1.5" C. or less. 
Freezing-point depression is related to the sum of the 
tension (suction) and osmotic pressure of water in 
soil. Calculate the total soil-moisture stress (SMS) 
in atmospheres from the observed freezing-point de- 
pression ( A7" )ofwater in soil cores by the relation, 

SMS=12AT 



Ayers and Campbell (1951), Campbell (1952), 
Richards and Campbell (1949), and Schofield and 
Bothelho da Costa (1938). 

Soluble Cations and Anions 

(7) Calcium and Magnesium by Titration 
With Ethyl en edi ami netetraacetate 
(Versenate) 



A. Ammonium chloride-ammonium hydroxide buffer 
solution. Dissolve 47.5 gm. of ammonium chloride 
in 570 ml. of concentrated ammonium hydroxide and 
make to 1 liter. 

B. Sodium hydroxide, approximately 4 N. Dis- 
solve 160 gm. of sodium hydroxide in 1 liter of water. 

C. Standard calcium chloride solution, 0.01 N . Dis- 
solve 0.500 gm. of pure calcium carbonate (calcite 
crystals) in 10 ml. of approximately 3 N (1 + 3) 



hydrochloric acid and dilute to a volume of exactly 
lliter. 

D. Eriochrome black T indicator. Dissolve 0.5 gm. 
of Eriochrome black T (F 241) and 4.5 gm. of 
hydroxylamine hydrochloride in 100 ml. of 95 percent 
ethanol. This indicator is available under several 
different trade names. 

E. Ammonium purpurate indicator. Thoroughly 
mix 0.5 gm. of ammonium purpurate with 100 gm. of 
powdered potassium sulfate. 

F. Ethylenediaminetetraacetate (Versenate) solu- 
tion, approximately 0.01 N. Dissolve 2.00 gm. of 
disodium dihydrogen ethylenediaminetetraacetate and 
0.05 gm. of magnesium chloride hexahydrate in water 
and dilute to a volume of 1 liter. Standardize the 
solution against reagent C, using the titration pro- 
cedures given below. The solution is standardized, 
using each of the indicators D and E, as the normality 
with E is 3 to 5 percent higher than with D . 

Procedure 

Pretreatment of soil EXTRACTS.-Ammonium 
acetate and dispersed organic matter, when present in 
appreciable amounts, must be almost entirely removed 
from soil extracts prior to titration with Versenate. 
Evaporation of an aliquot of the soil extract to dryness 
followed by treatment with aqua regia (3 parts cone. 
hydrochloric acid + 1 part cone, nitric acid), and a 
second evaporation to dryness usually suffices for the 
removal of ammonium acetate and organic matter. 
Very dark colored soil extracts may require additional 
treatment with aqua regia. Dissolve the residue in a 
quantity of water equal to the original volume of the 
aliquot taken for treatment. 

CALCIUM. -Pi pet a 5-to25-ml. aliquot containing 
not more than 0.1 meq. of calcium into a 3- or 4-inch 
diameter porcelain casserole. Dilute to a volume of 
approximately 25 ml. Add 0.25 ml. (5 drops) of 
reagent B and approximately 50 mg. of E. Titrate with 
F, using a 10-ml. microburet. The color change is 
from orange red to lavender or purple. When close 
to the end point, F should be added at the rate of about 
a drop every 5 to 10 seconds, as the color change is not 
instantaneous. A blank containing B, E, and a drop 
or two of F aids in distinguishing the end point. If the 
sample is overtitrated with F, it may be back-titrated 
with C. 

Calcium PLUS MAGNESIUM. -Pi pet a 5-to25-ml. 
aliquot containing not more than 0.1 meq. of calcium 
plus magnesium into a 125-ml. Erlenmeyer flask. 
Dilute to a volume of approximately 25 ml. Add 0.5 
ml. (10 drops) of reagent A and 3 or 4 drops of D. 
Titrate with F, using a 10-ml. microburet. The color 
change is from wine red to blue or green. No tinge of 
the wine-red color should remain at the end point. 

Calculations 

Milliequivalents per liter of Ca or Ca + Mg — (ml. of 
Versenate solution used X normality of Versenate solu- 
tion as determined by appropriate indicator X 1,000) / 
(ml. in aliquot). 



SALINE AND ALKALI SOILS 



95 



Remarks 

Iron, aluminum, and manganese, when present in 
concentrations greater than 20 p. p. m., and copper, 
when present in concentrations greater than several 
tenths of a p. p. m., interfere with the performance of 
the Eriochrome black T indicator. Usually the con- 
centrations of these metals in water and ammonium 
acetate extracts of soils of arid regions are insufficient 
to cause interference. If interference is encountered, it 
may be overcome as described by Cheng and Bray 
(1951) . 



Cheng and Bray (1951), Diehl and coworkers 
(1950). 

(8) Calcium by Precipitation as Calcium 
Oxalate 

Apparatus 
Centrifuge and 12-ml. conical tubes. 

Reagents 

(Keep reagents B, C, D, and E in Pyrex bottles.) 

A. Methyl orange, 0.01 percent in water. 

B. Hydrochloric acid, approximately 6 N (1+ 1). 

C. Oxalic acid, approximately 0.2 N. Dissolve 12.6 
gm. of oxalic acid di hydrate in water and make to 1 
liter. 

D. Ammonium hydroxide, approximately 7 N 

(i+i). 

E. Ammonium hydroxide in ethanol and ether. Mix 
20 ml. of cone, ammonium hydroxide with 980 ml. of a 
mixture of equal volumes of ethanol, ether, and water. 

F. Perchloric acid, 4 N. Dilute 340 ml. of 70 percent 
perchloric acid or 430 ml. of 60 percent perchloric acid 
to lliter. 

G. Nitro-ferroin indicator (5-nitro-l,10-phenanthro- 
line ferrous sulfate solution, 0.001 M). 

H. Ammonium hexanitrate cerate, 0.01 N in per- 
chloric acid, 1 N. Dissolve 5.76 gm. of ammonium 
hexanitrate cerate in 250 ml. of 4 N perchloric acid and 
dilute to 1 liter. The reagent should be standardized 
in the following manner: Pipet 5 or 10 ml. of fresh 
standard 0.01 N sodium oxalate into a small beaker 
containing 5 ml. of reagent F, add 0.2 ml. of G, and 
titrate with the cerate solution to the pale-blue end 
point. Determine a blank titration correction on a 
similar sample minus the oxalate solution. The milli- 
liters of oxalate used multiplied by 0.01 and divided 
by the corrected milliliters of cerate provide the nor- 
mality of the cerate. Do not attempt to adjust the solu- 
tion to exactly 0.01 N. Restandardize each time the 
reagent is used if more than 2 days have elapsed since 
the last standardization. Keep in a dark bottle away 
from light. 



Procedure 

Pipet an aliquot containing 0.005 to 0.08 meq. of 
calcium into a 12-ml. conical centrifuge tube, dilute or 
evaporate 14 to 5 ml., and add 1 drop of reagent A, 2 
drops of B, and 1 ml. of C. Heat to the boiling point 
in a water bath. While twirling the tube, add D drop 
wise until the solution just turns yellow. Replace in 
the bath, and, after 30 min., cool the tube in air or in 
water. If necessary, add more D to keep the solution 
just yellow. 

Centrifuge at RCF= 1,000 for 10 min. Carefully de- 
cant the supernatant liquid into another 12-ml. conical 
centrifuge tube and save for the magnesium determina- 
tion. Stir the precipitate and rinse the sides of the 
tube with a stream of 5 ml. of reagent E blown from a 
pipet. Centrifuge at RCF = 1,000 for 10 min. Decant 
and drain the tube by inversion on filter paper for 10 
min. Wipe the mouth of the tube with a clean towel 
or lintless filter paper. 

Blow into the tube 3 ml. of reagent F from a pipet. 
When the precipitate is dissolved, add 0.1 ml. of G. 
Titrate with H from a 10-ml. microburet to the pale- 
blue end point. If more than 5 ml. of H is required, 
transfer the sample to a small beaker and complete 
the titration. Determine the blank correction in the 
same manner ; it is usually about 0.03 ml. 

Calculations 

Milliequivalents per liter of Ca= (corrected ml. of 
cerate solution X normality of cerate X 1,000) /(ml. in 
aliquot) . 



Reitemeier (1943) . 

(9) Magnesium by Precipitation as Magne- 
sium Ammonium Phosphate 

Apparatus 

Centrifuge, 12-ml. conical tubes, and photoelectric 

colorimeter. 

Reagents 

A. Ammonium chloride, 3 percent solution. Dis- 
solve 3 gm. of ammonium chloride in water and dilute 
to 100 ml. Filter before use. 

B. Ammonium dihydrogen phosphate, 5 percent solu- 
tion. Dissolve 5 gm. of ammonium dihydrogen phos- 
phate in water and dilute to 100 ml. Filter before use. 

C. Phenol phthalein, 1 percent in 60 percent ethanol. 



14 Evaporation operations carried on with centrifuge tubes in 

a water bath may be speeded up by the use of an air blower. 
For this, a bank of glass nozzle-tubes in an array to match 
positions in the centrifuge tube rack is supplied with air from 
a compressed air system. A stream of air is thus introduced 
into each drying tube. 



96 



AGRICULTURE HANDBOOK 60, U. S. DEPT. OF AGRICULTURE 



D. Ammonium hydroxide, cone. 

E. Ammonium hydroxide in ethanol and ether. Mix 
20 ml. of cone, ammonium hydroxide with 980 ml. of 
a mixture of equal volumes of ethanol, ether, and water. 

F. Magnesium sulfate solution, approximately 0.01 
N, standardized. This is best prepared by dilution of a 
more concentrated solution of magnesium sulfate that 
has been standardized by gravimetric determination of 
magnesium (Method 78). 

G. Sulfuric acid. Approximately 5 N (1-1-6). 

H. Ammonium vanadate, 0.25 percent solution. 
Dissolve 2.5 gm. of ammonium vanadate in 500 ml. of 
boiling water, cool somewhat, and then add 60 ml. of 
reagent G. Cool to room temperature and dilute to 1 
liter. Store in a brown bottle. 

I. Ammonium molybdate, 5 percent solution. Dis- 
solve 50 gm. of ammonium molybdate in 1 liter of water. 
Store in a brown bottle. 

Procedure 

To the 12-ml. conical centrifuge tube containing the 
calcium-free sample from Method 8, add 1 ml. each of 
reagents A and B and 1 drop of C. Heat to 90" C. in 
a water bath and then add D until permanently pink. 
After 15 min., add an additional 2 ml. of D. Stopper 
and let stand overnight. 

Centrifuge at RCF= 1,000 for 10 min., decant care- 
fully, drain on filter paper for 10 min., and wipe the 
mouth of the tube with a clean towel or lintless filter 
paper. Wash the precipitate and sides of the tube with 
a stream of 5 ml. of reagent E from a pipet equipped 
with a rubber bulb or by a similar arrangement. Cen- 
trifuge at RCF= 1,000 for 5 min., decant, drain for 5 
min., and wipe the mouth of the tube. Repeat this 
washing procedure once. 

Pipet 10 ml. of reagent G into the tube and twirl for 
a few seconds. After 5 min. wash the contents into a 
100- ml. volumetric flask. Dilute to about 60 ml. and 
pipet 10 ml. each of H and I into the flask while twirl- 
ing rapidly. Dilute to the mark and mix. After 10 
min. measure the difference in light transmission of the 
sample and water, using optical cells and a 460-m/x 
filter. 

Starting at the beginning of the Procedure above, 
prepare a photometer calibration curve on semiloga- 
rithmic graph paper, for 0, 0.5, 1, 2, 3, 4, and 5 ml. of 
reagent F. One ml. of 0.2 N oxalic acid should beadded 
to each tube of standard before precipitating the mag- 
nesium. The amount of magnesium in the aliquot is 
obtained by simple interpolation on the curve. 

Calculations 

Milliequivalents per liter of Mg= (meq. of Mg found 
by interpolation X 1,000)/ (ml. in Ca aliquot X 0.98) . 
The factor of 0.98 corrects for magnesium lost in the 
washings from the calcium precipitate. 



(10) Sodium 

(10a) Sodium by Flame Photometer 
Apparatus 

Perkin-Elmer model 52 flame photometer with acety- 
lene or propane burner. 



Kitson and Mellon (1944), Reitemeier (1943). 



A. Ammonium acetate, approximately 1 N. To 700 
or 800 ml. of water add 57 ml. of cone, acetic acid and 
then 68 ml. of cone, ammonium hydroxide. Dilute to 
a volume of 1 liter and adjust to pH 7.0 by the addition 
of more ammonium hydroxide or acetic acid. 

B. Sodium chloride, 0.04 N. Dissolve 2.338 gm. 
of dry sodium chloride in water and dilute to exactly 
1 liter. 

C. Sodium chloride, 0.04 N in 1 N ammonium ace- 
tate. Dissolve 2.338 gm. of dry sodium chloride in re- 
agent A. Dilute to exactly 1 liter with additional A. 

D. Lithium chloride, 0.05 N. Dissolve 2.12 gm. of 
dry lithium chloride in water and dilute to exactly 
1 liter. 

Procedure 

Using reagents B and D prepare a series of standard 
sodium chloride solutions, each containing the same 
concentration of lithium chloride. Prepare a similar 
series of standard sodium chloride solutions, using 
reagents C and D, and use A for dilution. Recom- 
mended concentrations of sodium chloride are 0, 0.2, 
0.4, 0.6, 0.8, 1, 2, 3, and 4 meq./l. The optimum con- 
centration of lithium chloride varies with individual 
flame photometers but is usually 5 to 10 meq./L 
Standard solutions made up with water are employed 
for the analysis of waters and water extracts of soils; 
whereas, standard solutions made up in ammonium 
acetate solutions are used for the analysis of ammonium 
acetate extracts of soils. Calibrate the flame photom- 
eter for operation over the concentration range to 1 
meq./ I. of sodium, using the first 6 standard solutions 
of the appropriate series. Use the first and the last 4 
solutions of the appropriate series to calibrate the in- 
strument for operation over the concentration range 
to 4 meq./l. of sodium. 

Pipet an aliquot of the solution to be analyzed, con- 
taining less than 0.2 meq. of sodium, into a 50-ml. 
volumetric flask. Add an amount of reagent D that, 
when diluted to a volume of 50 ml., will give a concen- 
tration of lithium chloride exactly equal to that in the 
standard sodium chloride solutions. Dilute to volume 
with water, or with A, if ammonium acetate extracts 
are being analyzed. Mix and determine the sodium 
concentration by use of the flame photometer and the 
appropriate calibration curve. 

Calculations 

Milliequivalents per liter of N a in water or extract= 
(meq./l. of N a as found by interpolation on calibra- 
tioncurvex 50)/ (ml. in aliquot) . 



SALINE AND ALKALI SOILS 



97 



(10b) Sodium by Precipitation as Sodium 
Uranyl Zinc Acetate 

Apparatus 

Centrifuge and 12-ml. conical tubes. 

Reagents 

A. Uranyl zinc acetate. Weigh 300 gm. of uranium 
acetate di hydrate, 900 gm. of zinc acetate di hydrate, 
and 10 mg. of sodium chloride into a large flask. Add 
82 ml. of glacial acetic acid and 2,618 ml. of water. 
Stir or shake until the salts are dissolved, leaving only 
a small amount of sodium uranyl zinc acetate precipi- 
tate. Filter before use. 

B. Acetic acid-ethanol. Mix 150 ml. of glacial acetic 
acid with 850 ml. of 95 percent ethanol. Shake with 
an excess of sodium uranyl zinc acetate crystals. Filter 
before use. SOdium uranyl zinc acetate crystals may 
be prepared as follows : Add 125 ml. of reagent A to 
5 ml. of 2 percent sodium chloride solution, stir, and 
after 15 min. collect the precipitate in a porous-bot- 
tomed porcelain crucible. Wash several times with 
glacial acetic acid, then several times with ether, and 
finally dry in a desiccator. 

C. Ether, anhydrous. 

Procedure 

Pipet an aliquot containing 0.003 to 0.07 meq. of 
sodium into a 12-ml. conical centrifuge tube. Evapo- 
rate on a water bath to 0.5 ml. Cool, add 8 ml. of 
reagent A, and mix by stirring with an aluminum wire 
bent into a loop. Let stand 1 hour. Centrifuge at 
RCF= 1,000 for 10 min. Decant and drain on filter 
paper for 10 min. Wipe the mouth of the tube with a 
clean towel or lintless filter paper. Suspend the pre- 
cipitate and wash the sides of the tube, using 5 ml. of 
B blown from a pipet equipped with a rubber bulb. 
Centrifuge for 10 min., decant, and drain for 1 min. 
Wipe the mouth of the tube. Wash with 5 ml. of C, 
but centrifuge for only 5 min. Decant carefully with- 
out draining. Repeat washing and centrifuging once. 
Clean the outside of tube with chamois, dry for an 
hour or more at 60" C, cool in a desiccator, and weigh. 
Add 10 ml. of water, stir with the wire until the sodium 
precipitate is dissolved, centrifuge for 5 min., decant 
carefully, and drain for 5 min. on filter paper. Suspend 
the insoluble precipitate and wash the sides of the tube 
with 5 ml. of B blown from a pipet. Centrifuge for 5 
min., and decant. Wash with 5 ml. of C, centrifuge for 
5 min., clean tube with chamois, dry for an hour at 60°, 
cool in a desiccator, and weigh. The difference between 
the two weights is the weight of the sodium precipitate. 

Calculations 

Milliequivalents per liter of Na = (gm. of Na precipi- 
tate X 650.2) / (ml. in aliquot) . 



Reitemeier (1943) . 



( 11) Potassium 

(11 a) Potassium by Flame Photometer 

Apparatus 

Perkin-Elmer model 52 flame photometer with acety- 
lene or propane burner. 

Reagents 

A. Ammonium acetate, approximately 1 N. To 700 
or 800 ml. of water add 57 ml. of cone, acetic acid and 
then 68 ml. of cone, ammonium hydroxide. Dilute to 
a volume of 1 liter and adjust to pH 7.0 by the addition 
of more ammonium hydroxide or acetic acid. 

B. Potassium chloride, 0.02 N. Dissolve 1.491 gm. 
of dry potassium chloride in water and dilute to a 
volume of exactly 1 liter. 

C. Potassium chloride, 0.02 N in 1 N ammonium 
acetate. Dissolve 1.491 gm. of dry potassium chloride 
in reagent A. Dilute to a volume of exactly 1 liter 
with additional A. 

D. Lithium chloride, 0.05 N. Dissolve 2.12 gm. of 
dry lithium chloride in water and dilute to 1 liter. 

Procedure 

Using reagents B and D, prepare a series of stand- 
ard potassium chloride solutions, each containing the 
same concentration of lithium chloride. Prepare a 
similar series of standard potassium solutions using 
reagents C and D, and use A for dilution. The concen- 
trations of potassium chloride are 0, 0.1, 0.2, 0.3, 0.4, 
0.5, 1, 1.5, and 2 meq./l. The optimum concentration 
of lithium chloride varies with individual flame photo- 
meters but is usually 5 to 10 meq./l. Standard solu- 
tions made up in water are employed for the analysis 
of waters and water extracts of soils; whereas, those 
made up in ammonium acetate solution are used for the 
analysis of ammonium acetate extracts of soils. Cali- 
brate the flame photometer for operation over the con- 
centration range to 0.5 meq./l. of potassium, using 
the first 6 standard solutions of the appropriate series. 
Use the first and the last 4 solutions of the appropriate 
series to calibrate the instrument for operation over the 
concentration range to 2 meq./l. of potassium. 

Pipet an aliquot of the solution to be analyzed con- 
taining less than 0.1 meq. of potassium into a 50-ml. 
volumetric flask. Add an amount of reagent D which, 
when diluted to a volume of 50 ml., will give a concen- 
tration of lithium chloride exactly equal to that in the 
standard potassium chloride solutions. Dilute to 
volume with water or with A, if ammonium acetate ex- 
tracts are being analyzed, mix, and determine the potas- 
sium concentration by use of the flame photometer and 
the appropriate calibration curve. 

Calculations 

Milliequivalents per liter of K in water or extract= 
(meg./. of K as found by interpolation on calibration 
curve X 50) / (ml. in aliquot) . 



98 



AGRICULTURE HANDBOOK 60, U. S. DEPT. OF AGRICULTURE 



( // b) Potassium by Precipitation as Po- 
tassium Dipicrylaminate 

Apparatus 

Photoelectric colorimeter, centrifuge, and 12-ml 
conical tubes. 

Reagents 

A. Lithium dipicrylaminate solution. Dissolve 1.65 
gm. of lithium carbonate in 250 ml. of water. Warm 
to 50" C. and then add 9 gm. of di pi cry I amine. After 
the di pi cry I amine has dissolved, filter and dilute 200 ml. 
of this solution to 1 liter. To the remaining portion of 
approximately 50 ml., add 0.25 gm. of potassium 
chloride. Separate and wash the resulting potassium 
dipicrylaminate precipitate with a few milliliters of 
water by means of a centrifuge. Add the potassium salt 
to the warm solution of lithium dipicrylaminate and 
shake for 30 min. Filter the solution before use. 

B. Potassium chloride, 0.010 N. Dissolve 0.7456 
gm. of dry potassium chloride in water and dilute to 
exactly 1 liter. 

C. Phenol phthalein, 1 percent in 60 percent ethanol. 

D. Sodium hydroxide, approximately 1 N. Dissolve 
40 gm. of sodium hydroxide in water and dilute to 1 
liter. 

Procedure 

Pipet an aliquot containing 0.005-0.035 meq. of 
potassium into a 12-ml. conical centrifuge tube. Add 1 
drop of reagent C and then D until pink. Evaporate to 
dryness. This insures removal of ammonium. Cool 
and then add exactly 2 ml. of A. Grind the salt residue 
in the bottom of the tube by means of a glass rod and 
allow 1 hour for precipitation. Centrifuge the tube at 
RCF^= 1,000 for 1 min. Remove a 0.2-ml. aliquot from 
the supernatant liquid by means of a blood pipet and 
dilute to a volume of 50 ml. Compare the light trans- 
mission in an optical cell through a 510-m/x filter with 
that of water in similar cell. Prepare a calibration curve 
for each set of samples by carrying a series of 0.5, 1, 
1.5, 2, 2.5, 3, 3.5 ml. of B through the same operations. 
The amount of potassium in the sample is found by 
interpolation on this curve, When plotted on a linear 
scale the curve should be slightly Sshaped. The tem- 
perature at which the calibration curve is prepared 
should be within 2" C. of that at which the unknown 
determinations are made. 

Calculations 

Milliequivalents per liter of K= (meq. of K in ali- 
quot as found by interpolation X 1,000) / (ml . in 
aliquot) . 

Reference 

Williams (1941). 



(12) Carbonate and Bicarbonate by Titra- 

tion With Acid 

Reagents 

A. Phenol phthalein, 1 percent in 60 percent ethanol. 

B. Methyl orange, 0.01 percent in water. 

C. Sulfuric acid, approximately 0.010 N, standard- 
ized. 

Procedure 

Pipet an aliquot containing 0.005 to 0.04 meq. of 
chloride into a 15-ml. wide-mouthed porcelain crucible 
or a small porcelain casserole. Chloride is specified 
here because the same sample is subsequently used for 
the chloride determination in Method 13. Add 1 drop 
of reagent A. If the solution turns pink, add C from a 
10-mL microburet dropwise at 5- second intervals until 
the color just disappears. Designate this buret reading 
asy. Add 2 drops of B and titrate to the first orange 
color. Designate the new buret reading as z. Savethe 
titrated sample for the chloride determination. 

An indicator correction blank using boiled water 
should be determined and applied if it is not negligible. 
The lighting should be adequate for the recognition of 
the various colors. The use of comparison color stand- 
ards at the correct end points is helpful. 

Calculations 

1. Milliequivalents per liter of C0 3 = (2yX nor- 
mality of H,S0 4 X 1, 000) /(ml. inaliquot). 

2. Milliequivalents per liter of HC0 3 =(z-2y) X nor- 
mality of H 2 S0 4 X l,000/( ml. in aliquot). 

Reference 

Reitemeier (1943) . 

(13) Chloride by Titration With Silver 

Nitrate 

Reagents 

A. Potassium chromate, 5 percent solution. Dis- 
solve 5 gm. of potassium chromate in 50 ml. of water 
and add 1 N silver nitrate dropwise until a slight per- 
manent red precipitate is produced. Filter and dilute 
to 100 ml . 

B. Silver nitrate, 0.005 N. Dissolve 0.8495 gm. of 
silver nitrate in water and dilute to exactly 1 liter. 
Keep in a brown bottle away from light. 

Procedure 

To the sample preserved from the carbonate-bicarbo- 
nate determination, add 4 drops of reagent A. While 
stirring, titrate under a bright light with B from a 10- 
ml. microburet to the first permanent reddish-brown 
color. The titration blank correction varies with the 
volume of the sample at the end point, and usually in- 
creases regularly from about 0.03 to 0.20 ml. as the 
vol u me i ncreases from 2 to 12 ml . 



SALINE AND ALKALI SOILS 



99 



Calculations 



Milliequivalents per liter of CI = (ml. of AgN0 3 — ml, 
of AgN0 3 for blank) X 0.005 X 1,000/ ( ml. in aliquot) . 



Reitemeier (1943). 

( 14) Sulfate 

(14a) Sulfate by Precipitation as Barium 
Sulfate 

Apparatus 

Centrifuge and 12-ml. conical tubes. 

Reagents 

A. Methyl orange, 0.01 percent in water. 

B. Hydrochloric acid, approximately 1 N. 

C. Barium chloride, approximately 1 N. Dissolve 
122 gm. of barium chloride di hydrate in water and 
dilute to 1 liter. 

D. Ethanol, 50 percent by volume. 

Procedure 

Pipet an aliquot containing 0.05 to 0.5 meq. of 
sulfate into a clean 12-ml. conical centrifuge tube of 
known weight. Dilute or evaporate to about 5 ml. Add 
2 drops of reagent A, then B dropwise until pink, and 
then 1 ml. of B in excess. Heat to boiling in water bath. 
While twirling the tube add 1 ml. of C dropwise. Re- 
turn to the hot water bath for 30 min. and then cool at 
least an hour in air. 

Centrifuge at RCF= 1,000 for 5 min. Carefully 
decant and let drain by inversion on filter paper for 10 
min. Wipe the mouth of the tube with a clean towel 
orlintless filter paper. 

Stir the precipitate and rinse the sides of the tube 
with a stream of 5 ml . of reagent D blown from a pipet. 
I f necessary, loosen preci pitate from bottom of tube by 
means of a wire bent in appropriate shape. Centrifuge 
for 5 min. and decant, but do not drain. Repeat this 
washing and decanting operation once. Wipe the out- 
side of tube carefully with chamois and do not subse- 
quently touch with fingers. Dry overnight in an oven 
at 105° C. Cool in a desiccator and weigh. 

Calculations 

Milliequivalents per liter of SO^ (mg. of BaS0 4 
precipitate X 8.568) / (ml. in aliquot) . 

(Note. Care must be taken in the preparation or 
concentration of the unknowns so as not to precipitate 
foreign material which might be weighed as barium 
sulfate. ) 



( 14b) Sulfate by Precipitation as Calcium 
Sulfate 

Apparatus 

Wheatstone bridge, conductivity cell, centrifuge, and 
50-ml. conical tubes. 

Reagents 

A. Acetone. 

B. Calcium chloride, approximately 1 N. Dissolve 
74 gm. of calcium chloride dihydrate in water and dilute 
tol liter. 

Procedure 

Pipet an aliquot containing 0.05 to 0.5 meq. of 
sulfate into a 50-ml. conical centrifuge tube. Dilute or 
concentrate to a volume of 20 ml. Add 1 ml. of reagent 
B and 20 ml . of A. Mix the contents of the tube and 
let stand until the precipitate flocculates. This usually 
requires 5 to 10 min. Centrifuge at RCF= 1,000 for 
3 min., decant the supernatant liquid, invert the tube, 
and drain on filter paper for 5 min. Disperse the 
precipitate and rinse the wall of the tube with a stream 
of 10 ml. of A blown from a pipet. Again centrifuge 
at RCF=lfi00 for 3 min., decant the supernatant 
liquid, invert the tube, and drain on filter paper for 5 
min. Add exactly 40 ml. of distilled water to the tube, 
stopper, and shake until the precipitate is completely 
dissolved. Measure the electrical conductivity of the 
solution, using Method 4b, and correct the conductivity 
reading to 25" C. Determine the concentration of 
CaS0 4 in the solution by reference to a graph showing 
the relationship between the concentration and the 
electrical conductivity of CaS0 4 solutions. This graph 
may be constructed by means of the following data 
from the International Critical Tables. 

Electrical 

conductivity 

at 25" C. 
CaSCX concentration (meq./l.): Mmhos/cm. 

1 0.121 

2 .226 

5 .500 

10 .900 

20 1.584 

30.5 2.205 

Calculations 

Milliequivalents per liter of S0 4 — (meq./l. of CaS0 4 

from electrical conductivity reading) X (ml. in aliquot/ 

ml . of water used to dissolve preci pitate). 



Bower and Huss (1948). 



100 



AGRICULTURE HANDBOOK 60, U. S. DEPT. OF AGRICULTURE 



( 15) Nitrate by Phenoldisulfonic Acid 
Apparatus 

Photoelectric colorimeter. 

Reagents 

A. Phenoldisulfonic acid. Dissolve 25 gm. of phe- 
nol in 150 ml. of cone, sulfuric acid, add 75 ml. of fum- 
ing sulfuric acid (13 to 15 percent SO,), and heat at 
100" C. for 2 hours. 

B. Potassium nitrate, 0.010 N. Dissolve 1.011 gm. 
of dry potassium nitrate in water and dilute to exactly 
lliter. 

C. Silver sulfate, 0.020 N. Dissolve 3.12 gm. silver 
sulfate in 1 liter of water. 

D. Ammonium hydroxide, approximately 7 N 

(1 + 1). 

E. Calcium oxide. 

Procedure 

First determine the concentration of chloride in an 
aliquot as directed under Method 13. Pipet another 
aliquot containing 0.004 to 0.04 meq. of nitrate into a 
25-ml. volumetric flask. Add an amount of reagent 
C equivalent to the amount of chloride present. Dilute 
to volume and mix. Transfer most of the suspension 
to a 50-ml. centrifuge tube and separate the precipi- 
tate by centrifuging. After transferring the solution to 
another centrifuge tube, flocculate any suspended or- 
ganic matter by adding about 0.1 gm. of E and clear by 
again centrifuging. PipetalO-ml. aliquot represent- 
ing 2/5 of the sample into an 8-cm. evaporating dish. 
Evaporate the aliquot to dryness, cool, and dissolve the 
residue in 2 ml. of A. After 10 min., add 10 ml. of 
water and transfer to a 100-ml. volumetric flask. M ake 
alkaline by the addition of D, dilute to volume, and 
mix. M easure the light transmission through a 460-m/x 
filter in an optical cell against that of water in a 
similar cell. 

Prepare a calibration curve by pipeting 0, 0.2, 0.4, 
0.8, 1.2, and 1.6 ml. portions of reagent B into evapo- 
rating dishes and treating as above omitting the addi- 
tions of C and E, and the clarifying procedure. 

Calculations 

Milliequivalents per liter of N0 3 = (meq. of NO, in 
aliquot as found by interpolation on NO, curve) X 
1,000/ (ml. in aliquot) . 

( 16) Silicate as Silicomolybdate 
Apparatus 

Photoelectric colorimeter. 

Reagents 

A. Ammonium molybdate, 10 percent solution. 
Dissolve 10 gm. of ammonium molybdate in water and 
dilute to 100 ml. 



B. Sulfuric acid, approximately 5 N (1 + 6) . 

C. Sodium silicate, 0.01 N. Dissolve 1.5 gm. of 
Na 2 Si0 3 -9H 2 in 1 liter of water. Determine the silicate 
(Si0 3 ) concentration of this solution, using a 100-ml. 
aliquot and Method 76a (ch. 8). Adjust the remaining 
solution to exactly 0.01 N by the addition of a calcu- 
lated amount of water. Store in a plastic bottle. 

Procedure 

Pipet an aliquot containing 0.005 to 0.05 meq. of 
silicate into a 50-ml. volumetric flask. Dilute to a 
volume of 40 to 45 ml. with water. Add 2 ml. of 
reagent A and then 1 ml. of B. Dilute to 50 ml., mix, 
and after 15 min. measure the light transmission 
through a 420-m/x filter in an optical cell against water 
in a similar cell. Prepare a calibration curve by carry- 
ing a series of 0, 1, 2, 3, 4, and 5 ml. of C through the 
same operations. 

Calculations 

Milliequivalents per liter of Si0 3 = (meq. of Si0 3 in 
aliquot as found by interpolation X 1,000) /(ml. in 
aliquot) . 



Snell and Snell (1936). 

(17) Boron 

Determine boron as directed in Method 73b. If the 
solution is colored, transfer an aliquot to a platinum 
dish, make alkaline with NaOH, reagent A, and evapo- 
rate to dryness in an oven at 95° C. Ignite over an 
open flame until the residue fuses. Cool, add 5 ml. 
dilute HC1, reagent C, and complete as suggested in 
Method 73b under paragraph, Boron Concentration 
Too Low. 

Exchangeable Cations 

(18) Exchangeable Cations 

Apparatus 

Centrifuge, 50-ml. round-bottom, narrow-neck 
centrifuge tubes, and reciprocating shaker. 



A. Ammonium acetate solution, 1.0 N. To 700 or 
800 ml. of water add 57 ml. of cone, acetic acid and 
then 68 ml . of cone, ammonium hydroxide. Dilute to 
a volume of 1 liter and adjust to pH 7.0 by the addition 
of more ammonium hydroxide or acetic acid. 

B. Nitric acid, cone. 

C. Hydrochloric acid, cone. 

D. Acetic acid, approximately 0.1 N . 

Procedure 

Ammonium acetate extractable cations : Samples for 
this determination should be approximately 4 gm. for 



SALINE AND ALKALI SOILS 



101 



medium- and fine-textured soils and 6 gm. for coarse- 
textured soils. Weigh samples to an accuracy of 1 
percent and correct for the air-dry moisture content. 
Place the sample in a centrifuge tube. Add 33 ml. of 
reagent A to the tube, stopper, and shake for 5 min. 
Remove the stopper and centrifuge at RCF= 1,000 until 
the supernatant liquid is clear. This usually requires 
5 min. Decant the supernatant liquid as completely as 
possible into a 100-ml. volumetric flask. Extract with 
A a total of 3 times by this procedure, decanting into 
the same flask. Dilute to volume, mix, and determine 
the amounts of the various extracted cations by flame 
photometric or chemical methods. Flame photometric 
analyses may be made directly upon aliquots of the 
extract. If chemical methods are to be employed for 
the determination of cations, pretreat the extract in the 
following manner: Transfer to a 250-ml. beaker and 
evaporate to dryness on a hot plate or steam bath. 
Wash down the walls of the beaker with a small quantity 
of water and again evaporate to dryness. Add 1 ml. 
of B and 3 ml. of C, evaporate, and dissolve the residue 
in 20 ml. of D. Filter through low-ash content filter 
paper into a 50-ml. volumetric flask, using water to 
wash the beaker and filter paper. Dilute to volume. 

Soluble cations: Prepare a saturated soil paste as 
described in Method 2, using a 200- to 1,000- gm. sam- 
ple of soil. The weight of soil will depend upon the 
number of cations to be determined, the analytical 
methods employed, and the salt content of the soil. 
Determine the saturation percentage by Method 27. 
Obtain the saturation extract as described under 
Method 3a and determine the soluble cation concentra- 
tions by flame photometric or chemical methods. 

Calculations 

Ammonium acetate extractable cations in meq./lOO 
gm.— (cation cone, of extract in meq./l.X10)/(wt. of 
sample in gm.) . 

Soluble cations in meq./100gm.= (cation cone, of 
saturation extract in meq./l.) X (saturation percent- 
age) /1,000. 

Exchangeable cations in meq./lOO gm. = (extractable 
cations in meq./lOO gm.) — (soluble cations in meq./ 
100 gm.). 

Reference 

Bower and others (1952). 

( 19) Cation-Exchange-Capacity 

Apparatus 

Centrifuge, 50-ml. round-bottom, narrow-neck cen- 
trifuge tub&, and reciprocating shaker. 

Reagents 

A. Sodium acetate solution, 1.0 N. Dissolve 136 
gm. of sodium acetate trihydrate in water and dilute 



to a volume of 1 liter. The pH value of the solution 
should be approximately 8.2. 

B. Ethanol, 95 percent. 

C. Ammonium acetate solution, 1.0 N. To 700 or 
800 ml . of water add 57 ml . of cone, acetic acid and then 
68 ml. of cone, ammonium hydroxide. Dilute to a 
volume of 1 liter and adjust to pH 7.0 by the addition 
of more ammonium hydroxide or acetic acid. 

Procedure 

Samples for this determination should be approxi- 
mately 4 gm. for medium- and fine-textured soils and 6 
gm. for coarse-textured soils. Weigh samples to an 
accuracy of 1 percent and correct for the air-dry 
moisture content. Place the sample in a centrifuge 
tube. Add 33 ml. of reagent A, stopper the tube, and 
shake for 5 min. Unstopper and centrifuge at 
RCF= 1,000 until the supernatant liquid is clear. This 
usually requires 5 min. Decant the supernatant liquid 
as completely as possible and discard. Treat the 
sample in this manner with 33-ml. portions of A a total 
of 4 times, discarding the supernatant liquid each time. 
Add 33 ml. of B to the tube, stopper, shake for 5 min., 
unstopper, and centrifuge until the supernatant liquid 
is clear. Decant and discard the supernatant liquid. 
Wash the sample with 33-ml. portions of B a total of 3 
times. The electrical conductivity of the supernatant 
liquid from the third washing should be less than 40 
micromhos/cm. Replace the adsorbed sodium from 
the sample by extraction with three 33-ml. portions of 
C and determine the sodium concentration of the com- 
bined extracts after dilution to 100 ml. as described 
under Method 18. 

Calculations 

Cation-exchange-capacity in meq./100gm.= (Na 
cone, of extract in meq./l. X 10) / (wt. of sample in 
gm.). 

Reference 

Bower and others ( 1952). 

(20) Exchangeable-Cation Percentages 

(20a) Exchangeable - Cation Percentages 
by Direct Determination 

Procedure 

Determine the exchangeable-cation contents and the 
cation-exchange-capacity, using Methods 18 and 19. 

Calculations 

Exchangeable-cation percentage= (exchangeable-cat- 
ion content in meq./lOO gm. X 100) /(cation-exchange- 



IWI I V-V^l H-V^l IV. Ill HIVU,/ JL.W ^1 

capacity in meq./lOOgm.) . 



102 



AGRICULTURE HANDBOOK 60, U.S. DEPT. OF AGRICULTURE 



(20b) Estimation of Exchangeable-Sodi- 
um-Percentage and Exchange- 
able-Potassium-Percentage From 
Soluble Cations 

Procedure 

Prepare a saturation extract of the soil as described 
under Methods 2 and 3a. Determine the calcium plus 
magnesium, sodium, and potassium concentrations of 
the saturation extract, using Methods 7, 10, and 11, 
respectively. 

Calculations 

Exchangeabl e-sod i u m- percentage 

100 ( - 0.0126 + 0.01475X) 
~" 1 + ( - 0.0126 + 0.01475x) 

where x is equal to the sodium-adsorption-ratio. 

Exchangeabl e-potassi um-percentage 

_ 1QQ (0.0360 + 0.1051-) 
" 1 +(0.0360 + 0.1051%) 

where % is equal to the potassium-ad sorption- ratio. 
The sodium-adsorption-ratio and the potassium-adsorp- 
tion-ratio are calculated as follows: 



Sodi um-adsorption-ratio= Na + / V (Ca++ +Mg ++ ) /2 



and 



Potassium-adsorption-ratio ^K + /V (Ca+++Mg ++ )/2 

where Na+, K + , Ca++, and Mg ++ refer to the concentra- 
tions of designated cations expressed in milliequivalents 
per liter. 

A nomogram, which relates soluble sodium and 
soluble calcium plus magnesium concentrations to the 
sodium-adsorption-ratio,-' is given in figure 27. Also 
included in the nomogram is a scale for estimating the 
corresponding exchangeable-sodium-percentage, based 
on the linear equation given in connection with figure 9 
(ch. 2) . To use this nomogram, lay a straightedge 
across the figure so that the line coincides with the 
sodium concentration on scale A and with the calcium 
plus magnesi um concentration on scale B. The sodium- 
adsorption-ratio and the estimated exchangeable-so- 
dium- percentage are then read on scales C and D, 
respectively. 

Supplementary Measurements 
(21) pH Determinations 

(21a) pH Reading of Saturated Soil Paste 

Apparatus 

pH meter with glass electrode. 

Procedure 

Prepare a saturated soil paste with distilled water 
as directed in Method 2 and allow paste to stand at least 



1 hour. Insert the electrodes into the paste and raise 
and lower repeatedly until a representative pH reading 
is obtained. 

(21b) pH Reading of Soil Suspension 

Procedure 

Prepare a soil suspension, using distilled water, shake 
intermittently for an hour, and determine pH reading. 

(21c) pH Reading of Waters, Solutions, 
Soil Extracts 

Procedure 

Determine pH reading by means of a glass electrode 
assembly with the solution in equilibrium with a known 
CO, atmosphere. 

Remarks 

Opinion varies as to the proper method for making 
pH readings. It is desirable to select a definite pro- 
cedure and follow it closely, so that the readings will 
be consistent and have maximum diagnostic value. The 
method used should be described accurately so as to aid 
others in the interpretation of results. 

The CO, status influences pH readings, and should 
be controlled or specified. Ordinarily, readings are 
made at the CO, pressure of the atmosphere. A special 
high-pH glass electrode should be used for pH values 
appreciably above 9.0. 

(22) Gypsum 

(22a) Gypsum by Precipitation With Ace- 
tone (Qualitative) 

Reagent 

Acetone. 

Procedure 

Weigh 10 to 20 gm. of air-dried soil into an 8-oz. 
bottle and add a measured volume of water sufficient 
to dissolve the gypsum present. Stopper the bottle 
and shake by hand 6 times at 15-min. intervals or agi- 
tate for 15 min. in a mechanical shaker. Filter the 
extract through paper of medium porosity. Place about 
5 ml. of the extract in a test tube, add an approximately 
equal volume of acetone, and mix. The formation of a 
precipitate indicates the presence of gypsum in the soil. 

Remarks 

The soil should not be oven-dried, because heat- 
ing promotes the conversion of CaS0 4 *2H 2 to 
CaSO 4 *0.5H 2 O. The latter hydrate has a higher 
solubility in water for an indefinite period following 
its solution. 



SALINE AND ALKALI SOILS 



103 



_+ 



Na 
Meq./l. 

250 A 



Ca^Mo*"" 1 " 



2 00- 



150- 



100- 



50- 




\ ^s/ 



A 



B 



Figure 27.-Nomogram for determining the SAR value of a saturation extract and for estimating the corresponding 

ESP value of soil at equilibrium with the extract. 



104 



AGRICULTURE HANDBOOK 60, U. S. DEPT. OF AGRICULTURE 



(22b) Gypsum by Precipitation With Ace- 

tone (Quantitative) 

Apparatus 

Centrifuge, 50-ml. conical centrifuge tubes, conduc- 
tivity cell, and Wheatstone bridge. 

Reagent 

Acetone. 

Procedure 

Transfer a 20-ml. aliquot of the filtered extract ob- 
tained as described in Method 22a into a 50-ml. conical 
centrifuge tube. Add 20 ml. of acetone and mix. Let 
stand until the precipitate flocculates. This usually re- 
quires 5 to 10 min. Centrifuge at RCF= 1,000 for 3 
min., decant the supernatant liquid, invert the tube, and 
drain on filter paper for 5 min. Disperse the precipi- 
tate and rinse the wall of the tube with a stream of 10 
ml. of acetone blown from a pipet. Again, centrifuge 
for 3 min., decant the supernatant liquid, invert the 
tube, and drain on filter paper for 5 min. Add exactly 
40 ml. of distilled water to the tube, stopper, and shake 
until the precipitate is completely dissolved. Measure 
the electrical conductivity of the solution, using Method 
4b, and correct the conductivity reading to 25" C. 
Determine the concentration of gypsum in the solution 
by reference to a graph showing the relationship be- 
tween the concentration and the electrical conductivity 
of gypsum solutions. This graph may be constructed 
by means of the following data from the International 
Critical Tables. 

Electrical conductivity 

at 25" C. 
CaS0 4 concentration (meq./l.): Mmhos/cm. 

1 0.121 

2 .226 

5 .500 

10 -- -- .900 

20 _ 1.584 

30.5 2.205 

Calculations 

Milliequivalents of CaS0 4 in aliquot = (meq./l. 
ofCaS0 4 from conductivity reading) x (ml. of water 
used to dissolve precipitate) /1,000. 

Milliequivalents of gypsum per 100 gm. of soil = 
100 X (meq. of CaS0 4 in aliquot) / (soil: water ratio x 
ml. of soil-water extract used) . 

Remarks 

Sodium and potassium sulfates when present in suf- 
ficiently high concentrations are also precipitated by 
acetone. The maximum concentrations of sodium sul- 
fate and of potassium sulfate that may be tolerated are 
50 and 10 meq./l., respectively. 

At a 1: 5 soil-water ratio, water will dissolve ap- 
proximately 15 meq. of gypsum per 100 gm. of soil. 
If it is found that the gypsum content of the soil ap- 



proaches 15meq./100 gm. by use of a 1: 5 soil-water 
extract, the determination should be repeated, using a 
more dilute extract. 



Bower and Huss (1948). 

(22c) Gypsum by Increase in Soluble Cal- 
cium Plus Magnesium Content 
Upon Dilution 

Procedure 

Determine the saturation percentage and obtain a 
saturation extract of the soil using Methods 27 and 3a. 
Prepare another water extract of the soil, using a mois- 
ture content sufficient to dissolve the gypsum present 
as described under Method 22a. Determine the cal- 
cium plus magnesium concentrations of the two ex- 
tracts by Method 7. 

Calculations 

Soluble Ca+Mg at the saturation percentage in 
meq./lOO gm. = (Ca+ Mg cone, of saturation extract 
in meq./ I.) X (saturation percentage) /1,000. 

Soluble Ca+Mg at the high moisture percentage in 
meq./lOO gm. = (Ca + Mg cone, of dilute extract in 
meq./l. )X (moisture percentage) /1,000. 

Gypsum in meq./lOO gm. of soil= (soluble Ca+Mg 
at the high moisture percentage in meq./lOO gm.) — 
(soluble Ca + Mg at the saturation percentage in 
meq./lOO gm.) . 



15 



(22d) Gypsum Requirement 

Reagent 



A. Approximately saturated gypsum solution of 
known calcium concentration. Place about 5 gm. of 
CaS0 4 -2H 2 and 1 liter of water in a flask, stopper, and 
shake by hand several times during a period of 1 hr., 
or for 10 min. in a mechanical shaker. Filter and de- 
termine the calcium concentration of a 5-ml. aliquot 
of the solution by Method 7. The calcium concentra- 
tion should be at least 28 meq./l. 

Procedure 

Weigh 5 gm. of air-dried soil into a 4-oz. bottle. 
Add 100 ml. of reagent A by means of a pipet. 
Stopper the bottle and shake by hand several times dur- 
ing a period of 30 min. or for 5 min. in a mechanical 
shaker. Filter part of the suspension and determine the 
calcium plus magnesium concentration of a suitable 
volume of the clear filtrate using Method 7. 



15 



SCHOONOVER, W. R. EXAMINATION OF SOILS FOR ALKALI. 

University of California Extension Service, Berkeley, California. 
1952. (Mimeographed.) 



SALINE AND ALKALI SOILS 



105 



Calculations 

Gypsum requirement, meq./100gm.™ (Ca cone, of 
added gypsum solution in meq./L- Ca + Mgconc. of 
filtrate in meq./l.)X 2. 

(23) Alkaline-Earth Carbonates (Lime) 

(23a) Alkaline-Earth Carbonates by Effer- 
vescence With Acid 

Reagent 

A. Hydrochloric acid, 3N ( 1 + 3). 

Procedure 

Place several grams of soil on a small watchglass. 
By means of a pipet add sufficient water to saturate the 
soil. This displaces most of the soil air so that its loss 
upon the addition of acid will not be confused with 
effervescence of lime. Add a few drops of reagent A to 
the soil and note any effervescence that occurs. The 
soil may be termed slightly, moderately, or highly 
calcareous in accordance with the degree of efferves- 
cence obtained. 

(23b) Alkaline-Earth Carbonates by Grav- 
imetric Loss of Carbon Dioxide 

Reagent 
A. Hydrochloric acid, 3 N (1 + 3). 

Procedure 

Pipet 10 ml. of reagent A into a 50-ml. Erlenmeyer 
flask, stopper with a cork, and weigh. Transfer a 1- 
to 10-gm. sample of soil containing 0.1 to 0.3 gm. of 
calcium carbonate to the flask, a little at a time, so as 
to prevent excessive f rothi ng. After effervescence has 
largely subsided, replace the stopper loosely and swirl 
the flask. Let stand with occasional swirling until the 
weight of the flask and contents does not change more 
than 2 or 3 mg. during a 30-min. period. The reaction 
is usually complete within 2 hours. Prior to weighing, 
displace any accumulated carbon dioxide gas in the 
flask with air. This is important and may be done by 
swirling with the stopper removed for 10 to 20 sec. 

Calculations 

Weight of CO, lost= (initial wt. of flask+ acid + 
soil) — (final wt. of flask + acid + soil). 

CaC0 3 equivalent in percent= (wt. of CO, lost X 
227.4) /wt. of soil sample. 

Remarks 

The accuracy of this method depends to a large ex- 
tent upon the sensitivity of the balance used for weigh- 
ing. Using a torsion-type balance capable of detecting 
weight differences of 2 to 3 mg., the relative error is 
about ± 10 percent. 

J59525 0-54-8 



(23c) Alkaline-Earth Carbonates From 
Acid Neutralization 

Reagents 

A. Hydrochloric acid, 0.5 N, standardized. 

B. Sodium hydroxide, 0.25 N, standardized. 

C. Phenol phthalein, 1 percent in 60 percent ethanol. 

Procedure 

Place 5 to 25 gm. of soil in a 150 ml. beaker, add 50 
ml. of reagent A by means of a pipet, cover with a 
watchglass, and boil gently for 5 min. Cool, filter, 
and wash all the acid from the soil with water. Deter- 
mine the amount of unused acid by adding 2 drops of C 
and back-titrating with B. 

Calculations 

CaC0 3 equivalent in percent= (meq. HC1 added — 
meq. NaOH used) X S/weight of sample in gm. 

Remarks 

The calculation gives the CaC0 3 equivalent. This 
is the amount of CaC0 3 required to react with the acid. 
This value usually is somewhat high, because soil con- 
stituents other than lime may react with the acid. 

(24) Organic Matter 

Apparatus 

Erlenmeyer flasks, 500-ml., thermometer, 200° C. 



A. Potassium dichromate, 1 N. Dissolve 49.04 gm. 
of potassium dichromate in water and dilute to 1 liter. 

B. Sulfuric acid, cone, containing silver sulfate. 
Dissolve 25 gm. silver sulfate in a liter of acid. 

C. Ferroin indicator (ortho-phenanthroline ferrous 
sulfate, 0.025 M) . Dissolve 14.85 gm.o-phenanthro- 
line monohydrate and 6.95 gm. ferrous sulfate in water 
and dilute to 1 liter. 

D. Ferrous sulfate, 0.5 N. Dissolve 140 gm. of 
FeS0 4 -7H 2 in water, add 15 ml. of cone, sulfuric acid, 
cool, and dilute to 1 liter. Standardize this solution 
daily against 10 ml. of reagent A, as directed in the 
procedure below. 

Procedure 

Grind the soil to pass 0.5-mm. screen, avoiding con- 
tact with iron or steel. Transfer a weighed sample, not 
exceeding 1.0 gm. and containing from 10 to 25 mg. of 
organic carbon, to a 500-ml. Erlenmeyer flask. Add 10 
ml. of reagent A followed by 20 ml. of B. Swirl the 
flask, insert thermometer, and heat gently so as to 
attain a temperature of 150° C. in a heating period of 
about 1 min. Keep contents of flask in motion in order 



106 



AGRICULTURE HANDBOOK 60, U. S. DEPT. OF AGRICULTURE 



to prevent local overheating, which results in error 
caused by thermal decomposition of dichromate. After 
the 150° temperature is reached, place the flask on an 
asbestos pad, and allow to cool. Add 200 ml. of water 
and 4 or 5 drops of C. Titrate with D until the color 
changes from green to red. 

Since some soils adsorb o-phenanthroline indicator, 
the titration may be improved by a prior filtration, 
using a rapid filter paper on a Buechner funnel. If 
more than 80 percent of the dichromate solution is 
reduced, the determination should be repeated with 
less soil. 

Calculations 

Organic carbon in percent= (meq. of K 2 Cr 2 7 
added- meq. of FeS0 4 used) X0.336/wt. of sample 
ingm. 

Organic matter in percent = organic carbon in per- 
cent X 1.72. 

Remarks 

This modification of Walkley's rapid method (1935, 
1947) for the determination of organic carbon in soils 
has been found to give approximately 89 percent re- 
covery of carbon, as compared to the dry-combustion 
method. The conversion factor 0.336 was obtained by 
dividing 0.003, the milliequivalent weight of carbon, by 
89 and multiplying by 100 to convert to percent. 
Chloride interference is eliminated by the addition of 
the silver sulfate to the digesting acid as indicated. 
N itrates up to 5 percent and carbonates up to 50 percent 
do not interfere. 



Walkley (1935,1947). 

(25) Total and External Ethylene Glycol 
Retention 

Apparatus 

Vacuum pump, Central Scientific Company Hyvac 
or equivalent. 

Vacuum desiccators, inside diameter 250 mm., with 
external sleeve or glass stopcock and porcelain plates. 

Muffle furnace with automatic temperature control. 

Aluminum moisture boxes, 2y 2 in. in diameter and 
% in. high, with lids. 



A. Hydrogen peroxide, 10 percent solution. 

B. Anhydrous calcium chloride, 8 or 12 mesh, 
technical. 

C. Phosphorus pentoxide. 

D. Ethylene glycol (Eastman). Redistill under re- 
duced pressure, discarding the first and last 10 percent 
of the distillate. 



Procedure 

Soil preparation. Grind the soil sample to pass a 
60-mesh sieve. The increase in surface area brought 
about by this degree of grinding is negligible. Treat 
approximately 10 gm. of the sieved soil with reagent A 
for the removal of organic matter (see Method 41). 
Transfer the treated soil to a 5- to 8-cm. diameter Buech- 
ner funnel fitted with filter paper and leach with several 
small portions of distilled water, using suction. Allow 
the soil to air-dry, then pass through a 60-mesh sieve. 

Total ethylene glycol retention. Weigh 2.10 gm. of 
the 60-mesh soil into an aluminum moisture box. The 
tare weight of the box and its lid should be known. 
Spread the soil evenly over the bottom of the box. 
Place the box in vacuum desiccator over about 250 gm. 
of reagent C, apply vacuum by means of a Hyvac or 
equivalent pump, and dry the soil to constant weight. 
This usually requires 5 to 6 hours. Determine the 
weight of vacuum-dried soil. By means of a pipet, 
having a tip drawn to a fine point, distribute 1 ml. of D 
dropwise over the soil surface. Place the box in a 
second vacuum desiccator over 250 gm. of B and allow 
to stand overnight to obtain uniform wetting of the soil. 
Connect the desiccator to a Hyvac pump and evacuate 
at a temperature of 25 ±2° C. until excess ethylene 
glycol is removed from the soil. Depending upon the 
temperature and vacuum conditions attained, this 
usually requires from 5 to 7 hours when 8 samples are 
present in a desiccator. I n practice, the box is weighed 
after 5 hours in the vacuum desiccator and at intervals 
of 1 hour thereafter until the loss of weight per hour 
interval is less than 3 or 4 percent of the weight of 
ethylene glycol remaining on the soil. The next to the 
last weight taken is used to calculate ethylene glycol 
retained. 

External ethylene glycol retention. Weigh exactly 
2.10 gm. of the 60-mesh soil into an aluminum moisture 
box. Spread the soil evenly over the bottom of the 
box and heat at a temperature of 600 ± 15" C. for 2 
hours in a muffle furnace having automatic temperature 
control. Remove the box, cover, cool in a desiccator 
containing reagent B, and weigh. Apply 1 ml. of D 
to the soil, let stand overnight, and remove the excess 
ethylene glycol by evaporation in vacuum as described 
previously for the determination of total ethylene 
glycol retention. 

Calculations 

Assuming that 3.1 X 10~ 4 gm. of ethylene glycol are 
required for the formation of a monolayer on 1 sq. m. 
of surface, as indicated by Dyal and Hendricks (1950), 
the formulas for calculation of total, external, and 
internal surface areas are as follows: 

Total surface area, m.Vgm.^wt. of ethylene glycol 
retained by unheated soil, gm./(wt. of vacuum-dried 

unheated soil, gm. X 0.00031). 

External surface area, m. 2 /gm. = wt. of ethylene 
glycol retained by heated soil, gm./( wt. of vacuum- 
dried unheated soil, gm. X 0.00031). 



SALINE AND ALKALI SOILS 



107 



Internal surface area= (total surface area) — (ex- 
ternal surface area). 

Remarks 

The Hyvac pump and desiccators are connected by 
means of tight-fitting vacuum rubber tubing. A glass 
tube filled with reagent B is inserted in the vacuum line 
to prevent undesirable vapors from entering the 
pump. The tube also permits the introduction of dry 
air into the desiccators to release the vacuum. High- 
vacuum stopcock lubricant should be used to seal the 
glass joints. 

The adequacy of the vacuum system for removing 
excess ethylene glycol can be checked by determining 
the rate of evaporation of this liquid from a free sur- 
face. The average rate of evaporation over a 5-hour 
period from an aluminum moisture box of the size 
specified above and containing ethylene glycol should 
beat least lgm. per hour. 

For greatest accuracy in the determination of internal 
surface area, removal of excess ethylene glycol from 
heated and unheated soil should be performed concur- 
rently. Four unheated and the corresponding 4 heated 
samples are ordinarily placed together in a desiccator. 
The occasional inclusion of a standard sample having 
a known retention value serves as a useful control on 
procedure. 

The anhydrous calcium chloride placed in the desic- 
cator to absorb ethylene glycol should be renewed after 
each set of 8 determinations. The phosphorus pent- 
oxide used for drying under vacuum may be used until 
it absorbs sufficient water to develop a syrupy 
consistency. 



(27a) Saturation 
Drying 

Procedure 



Percentage From Oven- 



Bower and Gschwend (1952), Dyal and Hendricks 
(1950,1952). 

Soil Water 

(26) Soil-Moisture Content 

Procedure 

Transfer a representative subsample of the soil to a 
tared can with lid. For accuracy, it is desirable where 
possible to use at least a 25-gm. sample. Weigh, dry 
to constant weight at 105" C, and weigh again. 

Calculations 

Moisture content in percent, P w = (loss in weight on 
drying) X 100/ (weight of the oven-dry soil). 

(27) Saturation Percentage 



Transfer a portion of the saturated soil paste, pre- 
pared according to Method 2, to a tared soil can with 
lid. Determine the moisture content by Method 26. 

Calculations 

Saturation percentage (SP) = (loss in weight on dry- 
ing) X 100/( weight of the oven-dry soil). 

(27b) Saturation Percentage From Vol- 
ume of Water Added 

Remarks 

When the air-dry moisture content of the sample is 
known, as it usually is when exchangeable-cation analy- 
ses are made, the saturation percentage can be de- 
termined as follows: 

Procedure 

Transfer a known weight of air-dry soil to a mixing 
cup. Add distilled water from a buret or graduated 
cylinder with stirring until the soil is saturated as 
described in Method 2. Record the volume of water 
added. 

Calculations 

Weight of oven-dry soil= (weight of air-dry soil) X 
100/(100+ air-dry moisture percentage). 

Total water = (water added) 4 (water in air-dry soil) 
= (weight of water added) + (weight of air-dry soil) — 
(weight of oven-dry soil). 

SP= 100 X (total weight of water) / (weight of oven- 
dry soil). 

(27c) Saturation Percentage From the 

Weight of a Known Volume of 
Paste 

Remarks 

By this method, the saturation percentage is calcu- 
lated from the weight of a known volume of saturated 
soil paste. It is assumed that the soil particles have a 
density of 2.65 gm./cm. 3 , and that the liquid phase has 
a density of 1.00 gm./cm A 

Apparatus 

Balance, accurate to 0.1 gm. 

A cup of known volume. This measurement can be 
combined with the soil-paste resistance measurement 



108 



AGRICULTURE HANDBOOK 60, U. S. DEPT. OF AGRICULTURE 



using the same loading of the Bureau of Soils electrode 
cup. 

Procedure 

Determine the volume and weight of the cup. Fill 
the cup with saturated soil paste, jarring it during filling 
to exclude air, and strike off level with the top. Weigh 
and subtract the cup weight to get the net weight of the 
paste. 

Calculations 

WOJX65V-W) 
2.6S(W-V) 

where SP= saturation percentage ; V= volume of 
saturated soil paste, in cm. 3 , =a constant; and JF= net 
weight of Fcm. 3 of saturated soil paste, gm. Calcula- 
tions are simplified by the use of a table or graph relat- 
ing values of W and SP for a given value of V. 



Wilcox (1951). 

(28) Infiltration Rate 
Remarks 

Infiltration rate (infiltration capacity) is the rate 
of water entry into the soil where water covers the 
surface at a shallow depth and downward flow into 
and through the soil is nondivergent. The latter condi- 
tion is satisfied by rainfall or if the ponded area is 
infinitely large. For practical purposes, the subsidence 
rate of the free-water surface in a large basin is taken 
as a measure of the infiltration rate. The effect of 
divergent flow increases as the ponded area decreases. 
If small basins or cylinders are used, it is difficult to 
determine the true infiltration rate. For soils in which 
permeability increases with depth, errors from flow 
divergence may be negligible; but, if the permeability 
decreases with depth, the effect of flow divergence may 
be considerable. Flow divergence that occurs with 
small plots or cylinders may be minimized by ponding 
water in a guard ring or border area around the plot or 
cylinder. 

If infiltration measurements are made under condi- 
tions where divergent flow may not be negligible, the 
water-intake rate should be reported as infiltration 
velocity and accompanied by a description of the 
measuring method. 

Under some conditions the evaporation rate may not 
be negligible and must betaken into account in infiltra- 
tion measurements. In small basins or where cylinders 
are used, evaporation may be minimized by covering 
the water surface with a film of oil . 

There is no single method best suited to all field con- 
ditions. Experience and judgment are required in ob- 
taining and evaluating infiltration measurements. 
(See discussion in chapter 2.) 



(28a) Basin 

Apparatus 

Gage for measuring water elevation, and watch. 

Procedure 

Pond water on an area of soil enclosed by dikes or 
ridges. Measure the rate of subsidence of the water 
surface with a staff gage (a linear scale standing in the 
water), hook gage, or water-stage recorder. 

The infiltration rate will depend on the time and 
depth of water that has entered the soil. 

Calculations 

A curve showing the depth of water that has entered 
the soil as a function of time can be plotted from the 
water elevation -and time readings or taken from a 
water-stage recorder. Average or i nstantaneous val ues 
of the infiltration rate can be taken from this curve, 
depending on the purpose of the measurement. Ex- 
press infiltration rate in centimeters per hour or in 
inches per hour. 

(28b) Cylinder 

Apparatus 

Cylinders 11 to 14 in. in diameter and 16 in. long. 
The cylinders can be rolled from 16-gage sheet iron. 
Butt-weld and grind the weld smooth. Reinforce the 
upper end with i^-in. by l-in. iron strip, welded to 
cylinder. Galvanize cylinders after fabrication. For 
ease in transportation, cylinders can be made with 
different diameters so that they will fit, one within 
another. 

Circular driving cap and hammer. Torch-cut the 
driving cap from ^-in. steel plate and screw in a ^-in- 
central rod to serve as the hammer guide. The hammer 
can consist of a 50- to 80-lb. block of iron. This should 
have a central pipe to slide on the guide rod of the cap. 
Attach crosshandles to the pipe. 

Hook gage or staff gage, watch, thin metal tamp, 
splash guard of rubber sheet or burlap, field source 
of water. 

Procedure 

Drive the cylinders into the soil to a depth of 6 or 8 
in. Alternatively, the cylinders can be jacked into the 
soil, if a heavy tractor or truck is available. Care 
should be exercised to keep the sides of the cylinder 
vertical and to avoid disturbance of the soil column 
within the cylinder. Tamp soil into the space between 
thesoil column and the cylinder. If this space is greater 
than y s in., the cylinder should be reset. Cover the 
soil with a splash guard and apply 4 to 6 in. of water. 
Record the elevation of the water surface and the time 
at convenient intervals. A staff gage is often satisfac- 



SALINE AND ALKALI SOILS 



109 



tory, but a hook gage should be used if the subsidence 
rate is low. Several adjacent cylinders are usually 
installed. These need not be carefully leveled if a 
mark is placed on each cylinder for locating the base of 
the hook gage. 

While the wetting front is in the cylinder, the water- 
subsidence rate corresponds to the infiltration rate. 
When the wetting front passes below the cylinder, more 
or less divergence of flow will occur and the subsidence 
rate then should be designated as intake rate or infil- 
tration velocity. Divergent flow is minimized by in- 
stalling cylinders in plots or within larger diameter 
rings in which the soil is kept flooded. 

Where desired, water-entry rates into subsurface soil 
layers can be measured by excavating to the desired 
depth before setting the cylinders. 

Calculations 

Express infiltration rate and infiltration velocity in 
centimeters per hour or in inches per hour, using values 
averaged over time intervals appropriate to the purposes 
of the measurement. 

(29) 1/10- Atmosphere Percentage 
Apparatus 

Pressure- pi ate apparatus. Retainer rings approxi- 
mately 1 cm. high and 6 cm. in diameter to hold at least 
25-gm. samples. Balance, drying oven, and moisture 
boxes. 

Remarks 

Install the pressure plates to be used for the test in 
a pressure cooker, fill the cooker with water, fasten 
the lid on the cooker, and measure the rate of outflow 
of water from the ceramic plates at a pressure of 15 
lb. in. -2 . This rate should be about 1 cc. per cm. 2 per 
hr. per atm. pressure difference or greater for satis- 
factory operation of the porous plates. Next check 
the pressure plates for entry value as follows: release 
the air pressure, empty excess water from the cooker 
pot and the plates, close the cooker pot, and apply a 
pressure of i/ 2 atm. or other appropriate value. After 
a few minutes, the outflow of water from the plate out- 
lets will cease and there should be no bubbling of air 
from these outlets, thus indicating that the entry values 
for the plates are above the value of the pressure 
applied to the pressure cooker. At the conclusion of 
the entry-value test, submerge the pressure cooker in 
water while the pressure is on or make other equivalent 
tests to make sure that there are no air leaks at the 
cooker gasket or attendant connections. Air leaks 
from the cooker cause troubles with air-pressure con- 
trol and may also cause serious errors in retentivity 
determinations through direct loss of water vapor from 
the soil samples. 



Procedure 

Prepare duplicate 25-gm. samples that have been 
passed through a 2-mm. round-hole sieve, using the 
subsampling procedure outlined in Method 1. Place 
the sample retainer rings on the porous plate. I n order 
to avoid particle-size segregation, dump all of the soil 
sample from each container into a ring and level. 
Allow the samples to stand at least 16 hours with an 
excess of water on the plate. Close the pressure cooker 
and apply a pressure of 100 cm. of water. Samples 
1 cm. high can be removed any ti me after 48 hours from 
initiating the extraction or when readings on a buret 
indicate that outflow has ceased from all of the samples 
on each plate. Some soils will approach equilibrium 
in 18 to 20 hours. Before releasing the air pressure in 
the pressure cooker, put a pinch clamp on the outflow 
tube for each plate. This prevents backflow of water 
to the samples after the pressure is released. To avoid 
changes in the moisture content of the samples, trans- 
fer the samples quickly to moisture boxes. Determine 
the moisture content by drying to constant weight at 
105° C. Express the moisture content as percent, dry- 
weight basis. 



Richards and Weaver (1944), and Richards 
(1949b). 

(30) ^-Atmosphere Percentage 

Apparatus 

Same as i n M ethod 29. 

Procedure 

Same as in Method 29, except that the extraction 
pressure is 345 cm. of water. 

( 3 1) 15-Atmosphere Percentage 

Apparatus 

Pressure-membrane apparatus with sausage-casing 
membrane. Rubber soil -retaining rings 1 cm. high and 
approximately 6 cm. in diameter that hold about 25 
gm. of soil. Balance, drying oven, and moisture boxes. 

Procedure 

Prepare duplicate 25-gm. samples that have been 
passed through a 2-mm. round-hole sieve, using the sub- 
sampling procedure outlined in Method 1. Moisten the 
cellulose membrane, install in the apparatus, and trim 
the edge by running a knife around the brass cylinder. 
Place the soil -retaining rings on the membrane. In 
order to avoid particle-size segregation, dump all of 
the soil sample from each sample container into one 



no 



AGRICULTURE HANDBOOK 60, U. S. DEPT. OF AGRICULTURE 



ring. Pouring out part of the sample and leaving part 
in the container will give a nonrepresentative sample. 
Level the sample in the ring, cover with a square of 
waxed paper, and allow the samples to stand at-least 16 
hours with an excess of water on the membrane. Re- 
move excess water from the membrane with a pipet or 
rubber syringe, close the pressure-membrane appara- 
tus and admit air to the soil chamber at a pressure of 15 
atm. (220 lbs. in." 2 ). 

After a few hours, there is a marked decrease in the 
rate of water outflow from the soil, the outflow rate 
then being limited mainly by the low capillary conduc- 
tivity of the soil rather than the low membrane per- 
meability. At this time, the soil samples have sufficient 
rigidity to resist plastic flow and compaction and so a 
41b. inr 2 pressure differential may be applied to the 
rubber diaphragm at the top of the soil chamber. This 
diaphragm action holds the sample firmly in contact 
with the membrane and considerably hastens moisture 
extraction for fine-textured soils that shrink appreci- 
ably. The diphragm is unnecessary for medium- and 
coarse-textured soils. 

Remove the samples any ti me after 48 hours from the 
commencement of the extraction or when the readings 
on an outflow buret indicate equilibrium has been 
attained. Most soils will approach hydraulic equili- 
brium with the membrane in 18 to 20 hours, but some 
soils may require a considerably longer time. In order 
to avoid changes in the moisture content, transfer the 
samples to moisture boxes as soon as possible after 
releasing the extraction pressure. Determine the mois- 
ture content by drying to constant weight at 105" C. 
Express moisture content as percent, dry-weight basis. 

Remarks 

Care must be taken to keep soil away from the lower 
gasket of the cell. Otherwise, gasket flow that occurs 
when the eel I is closed may press sand particles into the 
membrane and cause leaks. 

References 

Richards (1947), Richards and Weaver (1944). 

(32) Moisture-Retention Curve 

Each sample, with disturbed or undisturbed struc- 
ture, is contained in a retainer consisting of a brass 
cylinder, a plastic lid, and a porous ceramic bottom 
plate, all held together with rubber bands. Various 
moisture equilibria and weighings are thus made pos- 
sible with a minimum of disturbance to the sample. 

Apparatus 

Pressure- pi ate apparatus, pressure-membrane appa- 
ratus, balance, drying oven, large straight-edged carv- 
ing knife, and aluminum moisture boxes with lids, ?>y 2 
in. diameter by 2 in. high. 



Soil sampling tube with retainer cylinders cut from 
brass tubing 2*4 in. outside diameter by 19-gage wall. 
The core retainer cylinders are 3 cm. high, and while 
in the sampling tube have guard rings 1 cm. high at 
each end. (See drawing of apparatus in the Appendix.) 

Plastic and ceramic disks serve as lids and bottoms 
for the core retainer. The lids are cut from y g in. 
transparent plastic sheet and are 2 l /± in. in diameter. 
The ceramic disks are 2 1 / 4 in. in diameter by % 6 in. 
thick, with a peripheral groove to attach two hooks 
formed from twisted wire at points on the disk 180° 
apart. The porous ceramic body should be like that 
used for tensiometer cups. The entry value should be 
greater than 1 atm., and the hydraulic conductivity 
should be equal to or greater than 8 X 10~ 4 cm./ hr. 

A layer of cheesecloth and sieved soil make capillary 
contact between the retainers and the control mem- 
branes. The cheesecloth should be treated with a bac- 
tericide such as Dowicide No. 4. The fraction of a loam 
soil that passes a 60-mesh screen makes a good capillary 
contact medium. 

A complete core-retainer set consists of a moisture 
box with lid, a brass cylinder, a plastic lid, two strong 
rubber bands, and a ceramic plate. All of the parts in 
a retainer set should bear the same identifying number. 
The tare weight of each retainer set with the ceramic 
disk saturated with water should be determined and 
recorded. 

Procedure 

Take the cores with the sampling tube when the soil 
is moist. Remove the l-cm. guard rings from either 
end of the 3-cm. retainer cylinder. Roughly trim the 
cores in the field and transport to the laboratory in 
the aluminum moisture boxes. Trim the cores accu- 
rately in the laboratory with the carving knife. Fasten 
the plastic lids and ceramic plates to the brass cylinders 
by stretching the rubber bands across the lids and 
attaching the bands to the hooks at the opposite edges 
of the ceramic plates. 

Place the core retainers on a porous brick with a 
free water surface 1 or 2 mm. below the surface of the 
brick. After 24 hours, wipe the excess water from the 
retainers, place each in its moisture box, and weigh. 
Replace the retainers on the brick with the water sur- 
face set for 10 cm. After 24 hours, weigh again. 
These two weighings will not represent equilibrium 
values, but high precision is usually not required at 
and 10 cm. of suction. Prepare the pressure- pi ate 
apparatus as indicated in Method 29. Spread approx- 
imately a 3-mm. layer of screened loam soil on the 
pressure plate and cover with a single layer of treated 
cheesecloth. Moisten the soil and cloth with water and 
set the retainers firmly in contact. Close the pressure 
cooker and adjust the pressure for the next suction 
value. 

Follow the approach to hydraulic equilibrium at 
each pressure by connecting the outflow tube from each 
plate or membrane to the lower end of a buret and 
recording the buret readings occasionally. When 



SALINE AND ALKALI SOILS 



111 



equilibrium is attained, clamp off the outflow tubes 
and release the air pressure in the cooker or membrane 
eel I . L ift the core retai ners from the membrane, brush 
off any adhering soil, place each in its numbered mois- 
ture box, and weigh. For a retention curve, weighings 
can be made at tensions of , 10, 30, 100, and 345 cm. 
of water and 1, 3, and 15 atm. Other suction values 
can be used, depending on the information desired. 

The porous-ceramic retainers used at the Laboratory 
have an entry value of 1 atm. and do not change ap- 
preciably in moisture content at suction values up to 
3 atm. Therefore, the gross tare for a core-retainer 
set is the same for all weighings at suction values up 
to and including 3 atm. At the 15-atmosphere equi- 
librium, the ceramic retainer is removed before the 
weighing, and a correspondingly different tare weight 
is used. Determine the weight of the soil core when 
oven-dried at 105" C. 

Calculations 

Determine the volume of the core retainer and calcu- 
late the bulk density of the soil in the core. From the 
gross weights at each suction, the tare weights, and 
the known weight of soil, calculate both the mass of 
water and the volume of water (numerically the same 
when c. g. s. units are used) in the core at each suction 
value. From the foregoing data, calculate the grams 
of water per 100 gm. of dry soil and the cubic centi- 
meters of water per 100 cm. 3 of soil at each suction 
value. The latter may be taken as the depth percentage, 
i. e., the depth of free water per 100 units of depth of 
soil. Plot these values on linear coordinates with 
moisture retention as the dependent variable, and 
suction or soil-moisture tension as the independent 
variable. 



Richards (1947, 1948, 1949b, 1952). 

(33) Field-Moisture Range 

Remarks 

Plants can grow in soil over a range of moisture 
contents referred to as the available range. The prac- 
tical upper boundary for this range, sometimes referred 
to as field capacity, is characteristic of the field situa- 
tion, and the best method for its determination is based 
on field sampling. The determination should be made 
after the soil has been wetted and the rate of down- 
ward drainage has decreased, but before appreciable 
moisture is lost from the profile by evaporation and 
root extraction. This determination loses significance 
or requires special interpretation if drainage is re- 
stricted or if a water table is close to the soil surface. 

Apparatus 

Soil tube or soil auger, watertight moisture boxes, 
balance, and drying oven. 



Procedure 

One to 3 davs after the soil pro>file is thoroughly 
wetted with rain or irrigation water, take samples by 
horizons, by textural layers, or at l-foot-depth inter- 
vals throughout the wetted zone. Determine the mois- 
ture content of the samples by drying to constant weight 
at 105" C. Express the results as moisture percentage, 
dry-weight basis, or as depth percentage if the bulk 
density can be determined. The available range for 
the soil at any given depth is then found by subtracting 
thel5-atm. percentage from the field determination of 
the upper limit of available water. The available range 
can be expressed either as a dry-weight percentage or as 
a depth percentage. 

(34) Hydraulic Conductivity 

(34a) Hydraulic Conductivity of Soil 
Cores 

Thin-walled cylinders or cans may be pressed into 
the soil in the field to obtain samples of soil of sub- 
stantially undisturbed structure. More often, soil cores 
are obtained in metal sleeves that fit into a sampling 
tube, and, after the samples have been taken, the sleeves 
serve as the core retai ners. Power-d riven machi nes are 
available for taking undisturbed cores of 4- and 6-in. 
diameter. Such cores are encased in the field for trans- 
portation and subsequent water-flow measurements. 
Various casing methods have been used, such as paint- 
ing the core with wax or plastic cement before and 
after wrapping in cloth. 

Procedure 

In the laboratory, the cores are mounted vertically 
and supported on a porous outflow surface such as 
sand or filter paper and metal screen. A shallow depth 
of water is usually maintained over the soil surface by 
a siphon tube from a constant-level reservoir. Flow 
tests should be conducted with water of the same quality 
as that which occurs in the field. If discharge rates 
are low, care must be taken to avoid errors arising 
from evaporation of the percolate. If possible, flow 
tests should be conducted at or near constant tem- 
perature. 

Where desirable, especially for long cores, manom- 
eters can be attached at various points along the core. 
These should be installed at transition zones between 
horizons or at textural discontinuities. 

Calculations 

Water flow takes place in accordance with the equa- 
tion : 

1 kA AL 

where Q is the volume of water passing through the 
core in time (*) , A is the area of the core, and k is the 
average hydraulic conductivity in the soil interval 



112 



AGRICULTURE HANDBOOK 60, U. S. DEPT. OF AGRICULTURE 



(AL) , over which there is a hydraulic head difference 
of AH. Solving for k gives k=QAL/AtAH.H.y- 
draulic conductivity (k) will be in centimeters per hour 
if/ is expressed in hours, Q in cm. 3 ,>4 in cm. 2 , and A// 
and AL are both in the same units. 



Bower and Peterson (1950), Kelley and coworkers 
(1948), Marsh and Swarner (1949), and Richards 
(1952). 

(34b) Hydraulic Conductivity of Dis- 
turbed Soil 

Apparatus 

Soil containers are made from 20-gage seamless brass 
tubing, 3 in. outside diameter, and 4 in. in length. 
The bottoms of the containers are machined from 20- 
gage brass sheet and are soldered into a recess or 
counterbore in the cylinders. The central outflow 
tubes are 2 in. long, are cut from y 2 in. outside diame- 
ter by 20-gage brass tubing, and are attached with 
solder. 

Supports for soil and filter paper consist of circles 
of 20-mesh or coarser bronze screen cut so as to fit 
loosely on the inside of the soil container. 

Packing block is made from a heavy wooden block 
approximately 4 by 4 by 8 in. A hole is made in the 
block to accommodate the outflow tube of the soil con- 
tainer, and guide rods are mounted in the block to keep 
the cylinder vertical and to insure square impacts. 
One rod is cut 2.5 cm. above the cylinder so that a 
finger placed over this rod gives a convenient index of 
height for the packing process. 

Sharkskin filter paper, rack for supporting a number 
of soil containers, constant-level water supply, siphon 
tubes to connect soil containers to water supply, gradu- 
ated cylinders, 2-mm. round-hole sieve, soil grinder, 
and mixing cloth. 

Procedure 

Air-dry the soil and pass it through a 2-mm. round- 
hole screen. A power grinder may be used for hard 
soils, but the grinding process must be standardized, 
with the plates set to reduce only the larger particles. 
Obtain representative 200-gm. subsamples in accord- 
ance with Method 1. Dump the entire subsample in one 
motion into the soil container that has been fitted with 
a screen and filter paper. This method of transferring 
the soil is used to prevent particle-size segregation. 
The cylinder containing the soil is dropped 20 times 
through a distance of 2.5 cm. onto the packing block. 
Place a filter paper on the soil surface and introduce 
water into the container with a minimum of soil dis- 
turbance. Record the time of application of water and, 
if possible, the time of the initial outflow. Collect the 
percolate in a suitable receptacle and measure the 
volume at convenient time intervals. Tests ordinarily 
are run until the volume of water that has passed 



through the soil corresponds to approximately 12 cm. 
of depth of water on the soil surface. Calculate hy- 
draulic conductivity and plot against accumulated 
equivalent depth of percolate. With soils having ex- 
tremely low percolation rates, an attempt should be 
made to obtain at least one flow measurement, and 
time rather than depth of water is used to determine 
when to discontinue tests on such soils. 

Remarks 

While, according to theory, neither the diameter nor 
the height of the soil column to be tested needs to be 
within prescribed limits, it has been found that with 
many soils satisfactory results are not obtained unless 
the height is less than the diameter of the soil column. 
This is particularly important if the soil swells ap- 
preciably on wetting. Experience indicates that the 
cylinder should have at least a 7.5-cm. diameter for a 
5-cm. depth of soil. 

Hydraulic-conductivity measurements should be 
made in the temperature range from 65" to 75" F. (18" 
to 24" C.) . For the most part, the effect of tempera- 
ture on hydraulic conductivity in this range is small 
compared with effects arising from such factors as 
quality of the water and the base status and salinity of 
the soil. The standard temperature for laboratory de- 
termination of hydraulic conductivity is usually taken 
as 68" F. (20" C.) . Corrections for viscosity effects 
on measurements at temperatures other than 68° F. 
can readily be calculated, but it has been observed that 
temperature has other and not always predictable ef- 
fects upon the hydraulic conductivity of soils in addi- 
tion to those arising from viscosity. 

The hydraulic gradient is usually set in the range 
from 1 to 4, although values as high as 10 do not seem 
to affect the results significantly. 

In general the water that will be used on the soil in 
the field should be used for the laboratory determina- 
tions, because small changes in water quality can pro- 
duce large changes in rate of moisture movement. 

Measurements are usually made in triplicate. The 
samples are discarded and the test repeated if the range 
of values is greater than 50 percent of the mean 
hydraulic-conductivity value. Between soils or treat- 
ments, average differences in conductivity of less than 
15 or 20 percent are not considered significant. 

Calculations 

Water flow takes place in accordance with the 
equation : 

* AL 

where Q is the volume of water passing through the 
material in time (t) ; A is the area of the soil column, 
and k is the average hydraulic conductivity in the soil 
interval ( AL) over which there is a hydraulic-head 
difference ( AH). Solving for hydraulic conductivity: 

a- <?A£ 

tAAH 



SALINE AND ALKALI SOILS 



113 



It should be noted that AH must be measured from 
the surface of water standing on the soil to the eleva- 
tion at which water will stand during the flow test in a 
riser or manometer connected at the bottom of the soil 
column. For experimental setups sometimes used, this 
elevation may be quite different from the elevation of 
the bottom of the soil column. The length of the soil 
column AL should be measured during or after water 
flow and not when the soil is dry. 



Christiansen (1947), Fireman (1944), and Richards 
(1952). 

(34c) Hydraulic Conductivity From Pie- 
zometer Measurements 

Equipment 

The piezometer pipe may be of any convenient diam- 
eter. The length will be governed by the depth at 
which measurements are to be made. The wall thick- 
ness should be as thin as practical to minimize soil 
disturbance during installation. Thin-walled electrical 
conduit 1 to 2 in. inside diameter, has been found suit- 
able for hydraulic-conductivity measurements at depths 
up to 10 ft. Other pieces of equipment needed for this 
measurement are: a screw-type soil auger having a 
free-fit inside the piezometer pipe; a hammer, such as is 
used for soil tubes or for steel fence posts, may be used 
for driving the pipe; a pump, such as a hand-operated 
pitcher pump, with a flexible hose attached to the inlet 
is needed to remove water and sediment from the pipe 
and the soil cavity; an electrical sounder is convenient 
for measuring the depth to the water surface within 
the pipe (see Method 35a) ; an ordinary watch is satis- 
factory for measuring time, except, if the rate of rise 
is rapid, two stop watches may be required to obtain 
a continuous rate-of-rise record; a soil-tube jack or 
other tube puller is useful in recovering the piezometer 
pipe. 

Remarks 

Hydraulic-conductivity measurements by this method 
are limited to soils below a water table. An auger 
hole is cased with a length of pipe and a cylindrical 
cavity is formed at the lower end of the pipe. Ground 
water flows into the cavity when water is pumped from 
the pipe, and the rate at which the water level rises in 
the pipe is a measure of hydraulic conductivity. Al- 
though the development of the equation is based upon 
an idealized condition of homogenous isotropic soil, 
this method may be used for determining the hydraulic 
conductivity of nonuniform soils and of individual soil 
layers. Information regarding water-table level and 
nature and position of subsoil layers should be available 
prior to installation of piezometer pipes to assist in 
determining proper placement of pipes and construc- 
tion of cavities. For most purposes, the extremities 



of the cavity should not be closer than one cavity length 
from either the top or bottom of the particular soil 
layer for which the determination is made. 

This method is applicable only where a cavity of 
known shape can be maintained throughout the test. 
In many fine-textured soils, cavities will stand without 
support, but in sands and other noncohesive materials 
a supporting porous structure may be required. 

Procedure 

Remove grass sod or debris from the soil surface 
and install the pipe to any desired depth by alternately 
augering and driving. Auger to a depth of 6 to 12 in. 
below the end of the pipe from within the pipe, then 
drive or push the pipe to the bottom of the drilled 
hole. This is done to minimize soil disturbance as the 
pipe is driven. When the pipe has been installed to the 
desired depth, auger out a cavity below the pipe. Cavity 
lengths of 4 to 8 in. have been found convenient, 
with pipes land 2 in. in diameter. The length of cavity 
can be accurately controlled by use of a screw clamp 
on the auger handle. The cavity should be formed 
with a minimum of disturbance to the surrounding 
soil. 

Remove seepage water and sediment from the cavity 
by pumping several times. Measure the depth to the 
water in the pipe after allowing enough time for the 
water to rise in the pipe to the equilibrium level. In 
highly permeable soils the equilibrium level may be at- 
tained in a few minutes; in some fine-textured soils 
several days may be required. Pump the water from 
the pipe and measure the rate at which ground water 
rises in the pipe. The rate of rise should be measured 
as soon as practicable after pumping, since, it is as- 
sumed, in the development of the theory, that the draw- 
down of the water table is negligible. Rate of rise may 
be measured at any point between the water-table level 
and the lower end of the pipe, but measurements near 
the equilibrium level should be avoided. The rise 
increment should be selected to give convenient and 
measurable time intervals. 

If hydraulic-conductivity determinations are desired 
at several depths, measurements can be made with the 
same pipe by successively augering to a greater depth 
following each determination. 

Calculations 

Hydraulic conductivity i calculated by use of the 
equation given by Kirkham (1946) as follows: 

2.30 it R 2 

k= A 7j_ — n log 10 (fcl/*2) 

where k is hydraulic conductivity; fi is the radius of 
tube; A is a geometrical factor (the A -fundi on) , which 
may be read from figure 28; h ± is the distance from the 
water table to the water level in pipe at time h;h 2 is 
the distance from the water table to the water level in 
pipe at time t 2 ; t 2 — t r is the time interval for water to 
rise from h^Xoh 2 . Hydraulic conductivity (k) will be 



114 



AGRICULTURE HANDBOOK 60, U. S. DEPT. OF AGRICULTURE 




75 



o 



50 



325 • 



i 

< 



2.5 5 7.5 10 

DIAMETER OF CAVITY - CM. 




2.5 5 7.5 
LENGTH OF CAVITY- CM. 



Figure 28.-Relation of the A-function to the length and diameter of the cavity for the piezometer method of measuring hydraulic 

conductivity. (Redrawn from Luthin and Kirkham, 1949.) 



in centimeters per hour if R and A are in centimeters; 
Ai and h 2 are both in the same units, and (t 2 — h) in 
hours. H owever, any consistent system of units may be 
used. For values of the A -function not shown in the 
illustrations see Luthin and Kirkham (1949). 

The hydraulic conductivity can also be calculated 
from an approximate equation that eliminates the use 
of logarithms. The constant inflow-rate equation of 
Kirkham (1946), slightly modified, is as follows: 

k _ 7T R 2 Ah 

where Ah is the increment of rise of the water level in 
the pipe in time z 2 "-£i;A av is the average head, i. e., 
Kv= {h 1 + h 2 )/2; and the other terms are as previously 
defined. 

This approximate equation is sufficiently accurate 
for the usual values of A h and A av and may be used to 
simplify calculations. The error introduced by using 
this equation is small if the ratio Ah/h x is small, but 
increases as the ratio increases. The error in k is less 
than 4 percent for ratios of A h/h, < 03 and less than 
10 percent for ratios as large as 0.7. 

References 

Johnson, F revert, and Evans (1952), Kirkham 
(1946), Luthin and Kirkham (1949), and Reeve and 
Kirkham (1951). 

(34d) Hydraulic Conductivity From Au- 
ger-Hole Measurements 

Equipment 

Soil auger; any convenient size may be used, but it 
should permit making a hole below the water table with 
a minimum of soil disturbance. Water-level sounder; 
an electrical sounder mounted on a frame or tripod 
is convenient for measuring depth to water in an auger 
hole. In large-diameter auger holes, water levels can 



be measured with a rule or tape. A rule attached to a 
float provides a convenient means for measuring the 
rate of rise of water in an auger hole. 

A hand-operated pitcher pump with a flexible hose 
attached to the inlet may be used to pump water and 
sediment from the auger hole. In addition, a stop 
watch is needed for time measurements. 

Remarks 

This method is limited to measurements in the soil 
profile below a water table and is applicable only 
where a cavity of known shape can be maintained 
throughout the test. 

Procedure 

Drill an auger hole to the desired depth below a 
water table with as little disturbance to the soil as 
possible. Insert the pump intake hose to the bottom 
of the auger hole and empty the cavity several times. 
This is done to remove suspended sediment and to 
reopen soil pores in the wall that may have been 
altered by the auger. Measure the depth to water in 
the hole when equilibrium with the surrounding ground 
water is attained. In highly permeable soils the equi- 
librium level may be reached in a few minutes; whereas, 
in some clays several days may be required. Pump the 
water from the hole and measure the rate at which the 
water rises in the hole while the water level is near 
the bottom of the auger hole or at the time that the 
auger hole is half full. The rate of rise should be 
determined as soon as practical after the water level is 
pumped down, since it is assumed in the development 
of the theory that the drawdown of the water table is 
negligible. A small rise increment should be used since 
the A-function varies as the hole fills up. The formula 
given below involves this assumption. 

Calculations 

Hydraulic conductivity is calculated by use of the 



SALINE AND ALKALI SOILS 



115 



equation given by Van Bavel and Kirkham (1949) as 
follows: 



&= 



ir a' 



Ah 

A (d--h) At 



whereA is the hydraulic conductivity; a is the radius of 
the auger hole; A is the A-function, a geometrical fac- 
tor which may be read from figure 29, for the case 
where the auger holeisempty and where it is half full; 
d is the depth of auger hole below the water table; 
h is the depth of water in the auger hole ; Ah is the 



increment of rise of the water level in 'the hole in the 
time interval At. 

Hydraulic conductivity (k) will be in centimeters 
per hour if a, d, h, and A are in centimeters and t is 
in hours. However, any consistent system of units 
may be used. 

In selecting values of the A-function (fig. 29), in- 
formation on the depth (s) to an impermeable layer 
below the bottom of the auger hole is required. When 
an impermeable layer occurs at a depth in the range 
from s=QXos=d, the A-function should be selected 



240 



220 



200 



180 



o 



160 



140 



I 120 

< 



too 



80 



60 



40 







1 



i HOLE HALF FULL (h/d= 0.5) 



HOLE EMPTY (h/d = 0) 



s/d = 0. 2 




s/d = 



s/d = 1.0 
s/d = 05 



s/d = 0. 2 



s/d = 



.0 4 .0 8 



J 2 



.16 



20 



.24 



RATIO - a/d 



Figure 29. — Relation of the value of the A-function to the ratio a/d, for the auger-hole method of measuring hydraulic conductivity: 
a, radius of the hole; d, depth of the hole below the water table; h, depth of water in the hole; s, depth of an impervious layer 
below the bottom of the hole. The A values in the figure are for auger holes having a radius equal to 5 cm. For any other 
radius (x) , multiply the A value read from the figure x/5. (Redrawn from Van Bavel and Kirkham, 1949.) 



116 



AGRICULTURE HANDBOOK 60, U. S. DEPT. OF AGRICULTURE 



from the curve for the nearest value of s/d. When 
s/d > 1, use the curve for s/d= 1. The depth(s) to 
an impermeable layer is not a critical factor for the 
usual values of u/d. See Van Bavel and Kirkham 
(1949) for discussion of errors involved when, with- 
out knowledge of the depth to an impermeable layer, 
arbitrary values of s/d are used. 

References 

Diserens (1934), Hooghoudt (1936), Johnson, Fre- 
vert, and Evans (1952), Kirkham and Van Bavel 
(1949), Reeve and Kirkham (1951), and Van Bavel 
and Kirkham (1949). 

(35) Hydraulic-Head Measurements in 
Saturated Soil 

(35a) Piezometers Installed by Driving 

Equipment 

Iron pipe, % in., galvanized or black, cut in 7, 10.5, 
14 ft., or other lengths as desired; hand-operated driv- 
ing hammer (Christiansen, 1943) or pneumatic driv- 
ing hammer (Donnan and Christiansen, 1944) ; rivets, 
structural iron, % in. in diameter by 1 in.; rivet 
punch-out rods (several lengths of % in. in diameter 
iron .pipe with male and female flush connections, or 
other rods to fit) ; 25 to 50 ft. of semirigid plastic 
tubing, 5/16 in. in diameter; 16 hand-operated bucket 
pump; 5-gal. water bucket; and carpenter's level. 

After installation it is necessary to measure the depth 
to water in the piezometer. This can be done with a 
steel tape or other sounding device. Tapes with a dark 
oxidized surface show the water-level mark readily, or 
chalk can be used to make the water mark more visible. 

If many readings are to be made, it is worth while to 
construct an electrical water-level sounder. For this, 
a length of flexible insulated wire is wound on a reel 
that has a socket for mounting on the top of the pie- 
zometer pipe. A straight segment of the wire slightly 
longer than 1 ft. should be exposed to view between 
the reel and the top of the pipe. The lower end of the 
wire is weighted with metal tubing to keep the wire 
taut, and the upper end is grounded to the reel and pipe 
through a battery and high-resistance voltmeter. The 
insulated wire is marked at 1-ft. intervals. Fractions 
of a foot can be read to the nearest 0.01 ft. from a 
scale attached to the reel mount. Readings are taken 
on the first mark on the wire appearing above the top 
of the pipe when the voltmeter indicates the lower end 
of the wire is at the water surface. 

Procedure 

With an iron rivet in lower end of pipe, drive first 

length of pipe into soil. Additional lengths can be 
added with standard pipe couplings as driving pro- 

16 Saran tubing, manufactured by the Dow Chemical Co., is 
suitable for this use and is often locally available at hardware 
stores. 



gresses until pipe reaches the desired depth. Leave pipe 
extending approximately 1 ft. above ground surface. 
If hydraulic-head readings are desired at several depths 
at a given location, drive pipes of different lengths into 
the soil, spacing the pipes laterally with a separation 
of about 1 ft. Use the carpenter's level to set the tops 
of all pipes to the same elevation. This makes it con- 
venient to record and interpret hydraulic-head read- 
ings. Pipe lengths up to 16 ft. long can be installed 
by driving if a stepladder is used. In some soils, the 
pipe can be pushed into the ground 5 or 6 ft. before 
driving is required so that21-ft. lengths can sometimes 
be used. Insert punch-out rod in pipe and punch rivet 
a distance of 3 to 6 in. out of the end of the pipe. 
Push the plastic tubing, previously marked with paint 
or tape to indicate the pipe length, to the bottom of 
the pipe and by pumping water through the tube with 
the hand pump, flush out a cavity 3 to 6 in. long below 
the end of the pipe. Soil material and water will re- 
turn to the surface in the annular space between the 
tubing and pipe. After the cavity at the base of the 
pipe is formed, test the piezometer for response rate 
by filling with water and observing the rate at which 
the water level drops. If the rate of change in the 
level of the water in the pipe is very low, repeat the 
flushing operation. In sands and gravels, the rate of 
drop may be so rapid that no overflow can be obtained 
during flushing; whereas, in clays the rate of drop may 
be so slow that it is hardly noticeable. In any event, 
the flushing should be repeated without unduly extend- 
ing the plastic tube below the end of the pipe until 
the rate of change of the water level in the pipe after 
filling is perceptible. The level of the water in the 
piezometer should then be allowed to come to equi- 
librium with the ground water. It is important to make 
this test of the responsiveness of each piezometer be- 
cause the reliability of readings depends directly upon 
the readiness with which the water level in the pipe 
respondsto hydraulic-head changes in the ground water 
at the bottom of the pipe. Piezometers should be re- 
tested for responsiveness periodically and reflushed, if 
necessary. 

In some soils, the rivet in the end may not be neces- 
sary. When the piezometer is driven, a soil plug from 
3 to 12 in. in length may form in the lower end of the 
pipe, which can be removed by the flushing operation. 
In many soils, this soil plug can be flushed out in 
much less time than is required to punch out the rivet. 

After the piezometers have been installed, flushed, 
and allowed to come to equilibrium with the ground 
water, the depth to water surface from the top of the 
pipe is measured and recorded. 

Remarks 

The hydraulic head of ground water at any given 
point, i. e., at the bottom of the pipe, is the equilibrium 
elevation of the surface of the water in the piezometer. 
This elevation can be referenced to any standard datum. 
All hydraulic-head readings in a single ground-water 
system or locality should be referenced to the same 



SALINE AND ALKALI SOILS 



117 



datum, mean sea level being commonly used. Water 
elevations at each site can be recorded as read from 
the top of the pipe. The elevations of the top of the 
pipe' and the adjacent soil surface are determined by 
standard surveying methods. 

The hydraulic gradient is the change in hydraulic 
head per unit distance in the direction of the maximum 
rate of decrease in head. The vertical component of 
the hydraulic gradient at a site where piezometers have 
been installed at several depths is equal to the differ- 
ence in the equilibrium elevation of the water surface 
in two pipes divided by the difference in the elevation 
of the cavities at the bottoms of the pipes. This is an 
average value for the vertical component of the hydrau- 
lic gradient in the depth interval. (See Method 36 for 
graphical procedures that are useful in the interpreta- 
tion of hydraulic-head readings.) 

References 

Christiansen (1943),Donnan and Christiansen 
(1944), and Richards (1952). 

(35b) Piezometers Installed by J etting 

Equipment 

Iron pipe, %-in. in diameter, galvanized or black, 
10.5-ft. lengths, threaded at both ends; power-driven 
pump, 300 to 600 lb./ in.', 10 to 15 gal./min. capacity 
with a water tank of 300-gal. capacity, truck- or trailer- 
mounted (an auxiliary 300-gal. water tank, truck- 
mounted, is also desirable) ; 25 to 50 ft. high-pressure 
hose, %-in. in diameter, with a swivel coupling for 
attachment to the pipe; driller's mud; and steel measur- 
ing tape or electrical sounder. 

Procedure 

The installation of piezometers by the jetting tech- 
nique makes use of the eroding and lubricating proper- 
ties of a stream of water issuing from the end of the 
pipe for opening a passage into the soil. Piezometers 
may be installed by hand or with simple hoisting and 
handling equipment, such as has been used in Coachella 
Valley, California, and described by Reger and as- 
sociates (1950). During installation, the pipe is oscil- 
lated up and down from 1 to 2 ft. to facilitate the 
jetting. Water and soil material in suspension return 
to the surface around the outside of the pipe. The 
return flow acts as a lubricant for the upward and 
downward movement of the pi pe and serves as a means 
for logging materials penetrated. An adjustable 
measuring tape used with the Coachella jetting rig 
serves to indicate depth of penetration to ±0.1 ft. If 
the jetting is done without a rig, the pipe should be 
marked at 1-ft. intervals to facilitate logging. 

An estimate of texture and consolidation of the ma- 
terial is made from (a) the nature of the vibrations in 
the pipe that are transmitted to the hands of the oper- 
ator, (b) the rate of downward progress, (c) exami- 
nation of sediments carried by the effluent, and (d) 



observation of color changes of the effluent. Logging 
subsurface layers by this method requires experience 
that can be gained and checked by jetting in profiles 
for which data on stratigraphy are available from 
independent logging procedures. 

Return flow may be lost and penetration may stop in 
permeable sands and gravels. A commercial prepara- 
tion, Aquagel, a form of driller's mud, was found by 
Reger and associates (1950) to be effective for main- 
taining return flow in coarse materials. Approximately 
10 lb. per 100 gal. of water was sufficient for jetting 
conditions encountered in the Coachella Valley. It is 
necessary to add this preparation to the water supply 
slowly and to agitate thoroughly as it is added. 

A record of the depth and nature of material pene- 
trated is kept as the jetting progresses. Where several 
hydraulic- head measurements are desired at different 
depths, the deepest pipe is usually installed first. The 
log from the first pipe serves for selecting depths at 
which additional pipes are to be installed. It is often 
desirable to terminate piezometers in sandy lenses to 
increase the rate at which they respond to hydraulic- 
head changes in the soil. Jetting is stopped immedi- 
ately as each pipe reaches the desired depth, so that 
excessive washing of material from around the pipe 
will not occur. The material in suspension settles back 
around the pipe arid usually provides a satisfactory seal. 
Several pipes that terminate in the soil at different 
depths may be installed as close as 1 ft. apart. Experi- 
ence has shown that, under most conditions, the effect 
of leakage along the pipe or from one pipe to another is 
negligible. 

After the piezometers are installed, they are flushed, 
reference elevations are set, and readings are made as 
outlined in Method 35a. (For details of jetting-equip- 
ment construction, refer to the article by Reger and 
others (1950) .) 

References 

Pillsbury and Christiansen (1947), Reeve and Jensen 
(1949), and Reger and others (1950). 

(35c) Observation Wells, Uncased or With 
Perforated Casing 

Equipment 

Soil auger; perforated tubing or pipe; steel tape, or 
electrical sounder. 

Procedure 

It is desired to measure depth to water table. An 
uncased auger hole can often be used to measure depth 
to water table. Where soils are sandy and will not 
stand or where a more permanent well is desired, an 
auger hole may be cased with perforated casing. Some- 
times it is necessary to install the casing during the 
augering process. 

Water-table observation wells are usually installed 
to a depth great enough to reach the minimum ex- 



118 



AGRICULTURE HANDBOOK 60, U. S. DEPT. OF AGRICULTURE 



pected position of the water table. As a result, observa- 
tion wells are sometimes installed to considerable 
depths and perforated throughout a portion or all of 
the underwater length. Under many conditions, water- 
level readings in such wells coincide with the water- 
table level, but if there is a vertical flow component of 
water in the soil, either upward or downward, water- 
level readings in an open or perforated casing well may 
not represent the true water-table level. Where vertical - 
flow conditions occur, the water level in a perforated 
cased well represents a steady-state flow condition 
within the well itself, and may not give useful informa- 
tion. Such a condition is more likely to occur where 
an observation well penetrates layers that differ greatly 
in permeability. Where such conditions occur or where 
there is any question about water-table readings, hy- 
draulic-head determinations should be made at several 
depths i n the profi le by the use of piezometers. 

The elevation of the water table can be determined 
by a graphical method as follows. Plot the elevation 
of the terminal points of the piezometers in the soil 
as a function of the corresponding pressure heads, i. e., 
the lengths of the columns of water standing in the pie- 
zometers. Extrapolate this curve to zero pressure-head 
to obtain the water-table elevation. Abrupt changes in 
soil permeability with depth in the vicinity of the water 
table complicate the use of this method and make it 
necessary to install piezometers at or near the water 
table. 

(36) Ground-Water Graphical Methods 

(36a) Water-Table Contour Maps 
Equipment 

Drafting instruments and supplies 

Procedure 

On a scale map of the area being investigated, write 
in the water-table elevations at locations at which water- 
table level measurements have been made. By stand- 
ard mapping procedures used for ground-surface con- 
tour plotting, i. e., interpolation and extrapolation, 
draw in lines of equal water-table elevations. The 
principles that apply in surface contour mapping also 
apply for water-table contours. Where slopes change 
abruptly, more points are required to locate the con- 
tours accurately. Conversely, in areas of little change 
in slope, measurement points may be farther apart. I n 
areas of rolling or varied topography where water 
tables in general follow surface slopes, the number of 
.data required to construct water-table contours may be 
prohibitive. A water-table contour line is the locus of 
points on the water-table surface for which the hydrau- 
lic head is constant. In a three-dimensional flow sys- 
tem, such a line represents the intersection ,of an equal 
hydraulic- head surface with the surface of the water 
table. 



Water-table contour maps provide direct visual in- 
formation on the slope of the water table, and it is to 
be expected that generally there is a horizontal move- 
ment of ground water in the direction of slope of the 
water table. In the absence of subsurface artesian 
conditions and if the areal application of water to the 
soil surface is uniform, a region of steep slope of the 
water table would be expected to occur where barriers 
to the horizontal movement of ground water occur or 
where the hydraulic conductance of the soil strata 
below the water table is low. On the other hand, areas 
of low slope in the ground-water table may indicate 
the presence of aquifers that permit the ready transfer 
of ground water in the horizontal direction. Such 
information is pertinent to the analysis and solution of 
drainage problems. 

(36b) Water-Table Isobath Maps 

Equipment 

Drafting instruments and supplies. 

Procedure 

On a scale map of the area, write in depths to water 
table from the ground surface at locations at which 
water-table and ground-surface elevations have been 
obtained. Construct isobath lines, i.e., lines of equal 
depth to water table, by the standard mapping pro- 
cedures that are used for ground-surface and water- 
table contour mapping, i. e., interpolation and extrapo- 
lation, and other procedures. Where either surface 
topography or water-table slopes change abruptly, more 
points of measurement are required for accurate con- 
struction of equal depth-to-water lines. 

Depth to water table may also be shown by circum- 
scribing areas within which depth to water table is in 
a specified range. On a scale map, note depths to 
water table as above. Select a convenient number of 
•depth ranges, such as to 2, 2 to 4, 4 to 10, 10 to 
20, > 20, and delineate areas within which depth to 
water table is in the designated ranges. Distinguish 
between areas with a Crosshatch, color, or other con- 
venient code system. Maps such as the foregoing pro- 
vide graphic information on the adequacy of drainage 
and, therefore, aid in showing areas in which artificial 
drainage may be needed. 

(36c) Profile Flow Patterns for Ground 
Water 

Equipment 

Drafting instruments and supplies. 

Procedure 

On a profile section showing the soil surface and 
available information on subsoil stratigraphy, write in 
hydraulic- head values at points where hydraulic-head 



SALINE AND ALKALI SOILS 



119 



120 



110L 

UJ w 

u. 
I 



_ _GROUND SURFACE 



2l00 

I- 

< 

> 

UJ 

_l 

UJ 

ui 90t 

o 

z 

UJ 
QC 
UJ 
U- 
UJ 

oc 80 



70^ 



o 
o 
o 




v^ 



»/// *\y#;*// , ^////A^/w^W^^'/P K\\\\yw \^^y/7\y 



t 



102 




LOWER END OF PIEZOMETERS 




WATER TABLE 



k 



TT 



101 



102 



o 



50 



40 



30 20 

WEST 



10 iO 

DISTANCE FROM DRAIN- FEET 



20 
EAST 



30 



4 



Figure 30.-Equal hydraulic-head lines below a water table on a profile section in the vicinity of an open drain. Example from Delta 
area, Utah. The direction of the hydraulic gradient is represented by arrows and indicates upward water movement from an 
underlying source. 



measurements have been made, i. e., points where 
piezometers terminate in the soil (fig. 30). By stand- 
ard methods, which are used for contour mapping, 
interpolation, and extrapolation, draw lines to connect 
points of equal hydraulic head. Convenient hydraulic- 
head intervals may be selected, extending over the range 
of measured values for hydraulic head. Usually an 
interval is selected that allows a number of equal 
hydraulic-head lines to be sketched on the same profile. 
The component of flow in the plane of the profile is 
normal to lines of equal hydraulic head, if the profile 
section is plotted to a 1 : 1 scale. With the 1 : 1 scale, 
flow lines can be sketched in at right angles to the 
equal hydraulic-head lines, with arrows to show the 
direction of flow. If the vertical scale is exaggerated, 
the relation between stream lines and equal hydraulic- 
head lines on the plotted profile is no longer orthogonal. 
Where the vertical and horizontal scales are not equal, 
therefore, the hydraulic- head distribution may be prop- 
erly plotted, but flow lines should not be indicated. 

For cases where hydraulic head changes in a vertical 
direction, indicating a vertical component of flow, the 
elevation of the water table can be determined by pie- 
zometers that terminate at the water-table level, or by 
extrapolation from a series of known points below the 
water table, as outlined in Method 35c. Draw equal 
hydraulic- head lines to intercept the water table at the 
respective equal hydraulic-head elevations. 



An equal hydraulic- head line may intercept the water 
table at any angle, depending upon the flow direction. 
The water table is not necessarily a flow line as is often 
assumed, although it may be. A component of upward 
flow that exists below the water table may continue 
upward through the soil above the water table to the 
soil surface by capillarity. Likewise, downward flow 
may occur in the unsaturated soil above a water table. 

References 

Christiansen (1943), Reeves and Jensen (1949). 

(36d) Water-Table Isopleths for Showing 
Time Variations in the Elevation 
of the Water Table 

Equipment 

Drafting instruments and supplies. 

Procedure 

A large seasonal variation in the water table often 
occurs in irrigated areas. In such cases it may be use- 
ful to show graphically the variations, both in space 
and time, by the use of water-table isopleths. 17 By this 

17 Private communication from M. Ram, Water Utilization 
Division, Ministry of Agriculture, Tel Aviv, Israel. 



120 



AGRICULTURE HANDBOOK 60, U. S. DEPT. OF AGRICULTURE 



method a series of observation wells is established on 
a straight line across the area under investigation and 
water-table elevations are recorded over a period of 
time. 

The graphical representation of the data is accom- 
plished as follows: On a vertical scale at the left margin 
of a sheet of tracing paper, make a time scale on which 
the dates are shown for the various sets of readings of 
the observation wells. Start the time scale near the 
top of the sheet with the initial set of readings. Draw 
horizontal constant-time lines across the sheet at the 
time values for the various sets of readings. Across 
the top of the sheet, draw a profile of the elevation of 
the soil surface along the line of observation wells. Use 
any convenient vertical scale and mark the location of 
the observation wells on the horizontal scale. Draw in 
horizontal lines representing convenient elevation inter- 
vals over the range of variation in the elevation of the 
water table and plot the water-table profile for the initial 
set of readings. Project the points of intersection of 
this profile curve with the elevation scale lines down- 
ward to the horizontal constant-time line of the initial 
set of readings. Place elevation numbers above these 
points on the constant-time line. Repeat this process, 
locating successive elevation points on successive con- 
stant-time lines for each set of well readings. Connect 
constant water-table elevation points on successive con- 
stant-time lines with smooth curves. These curves are 
called isopleths and show the variation with time of 
the points of equal water-table elevation along the line 
of water-table observation wells. 

The sources of ground water as well as subsurface 
stratigraphy must be taken into account in the inter- 
pretation of isopleths. The method provides a con- 
venient graphical summary of water-table observations 
and can be used to advantage in showing the rate of 
subsidence of the water table following an irrigation 
season. This information relates directly to the drain- 
ability of soils. 

Physical Measurements 
(37) Intrinsic Permeability 

(37a) Permeability of Soil to Air 

Apparatus 

The apparatus for this measurement is shown in 
figure 31. Compressed air is admitted through a cal- 
cium chloride drying tube to an airtight tank of con- 
stant volume. An outflow tube leads to a water 
manometer and to the soil sample container. The soil 
sample container consists of a tinned iron can with an 
extension made from a 4-cm. section of brass tubing 
counter-bored to give a snug fit on the top of the can. 
Punch an outlet hole, approximately 5/32 in. in diam- 
eter in the bottom of the can. Use a disk of brass 
screen, 20- or40-mesh, with 2 layers of fiberglass sheet 



CALCIUM CHLORIDE 
DRYING TUBE 



>: 



AIR STORAGE 
TANK 



WATER 
MANOMETER 



SOIL SAMPLE 
CONTAINER 



LJ 



-I- wu 



□ 



H 



Figure 31.-Apparatus using air flow to measure the intrinsic 
permeability of soil by Method 37a. The manometer read- 
ings yi and y 2 represent successive heights of the free-water 

surface above the rest position. 

as a filter in. the bottom of each can. The soil-packing 
machine, mentioned below, is useful for this measure- 
ment. 

Remarks 

This method for measuring air permeability can be 
used for either disturbed or undisturbed samples. The 
following procedure is for disturbed soils. In order 
to get consistent results for comparing one soil with 
another and to determine the effect of various treat- 
ments, a standard procedure for preparing and packing 
the soil must be followed. Make determinations in 
triplicate. 

Procedure 

Pass air-dried soil through a wire-mesh sieve with 
1 -mm. openings. Obtain representative subsamples as 
outlined in Method 1. Attach the brass cylinder to the 
top of a can and fill the container about three-fourths 
full of soil. Dump the soil, which has been well mixed, 
into the container rather than by pouring or scooping. 
With a spring-load of 3-kg. wt. on top of the soil, drop 
the container 200 times on a solid block of wood from 
a height of 2.5 cm. A cam-operated mechanical drop- 
per has beeh used for this purpose. Remove the brass 
cylinder from the can and use a spatula to strike the 
soil off level with the top of the can. Cover the soil 
with a disk of filter paper, place a lid on the can, and 
complete the seal with a tight rubber band or beeswax. 
Connection to the air source is made by means of a short 
piece of copper tubing soldered to the lid of the can. 
Pass compressed air through the drying tube to the 
tank until a manometer displacement of 40 to 50 cm. 
of water is attained. Record the air temperature in 
the tank and measure the rate of drop of the ma- 
nometer level as air is allowed to flow from the tank 
through the soil sample. It is desirable to allow an 
initial 10-cm. drop of the manometer level before 
height and time readings are started. 

Calculations 

The intrinsic permeability of the soil using air is 
given by the equation : 



SALINE AND ALKALI SOILS 



121 



A' a = 2.30 LVS v 

A Pa 
in which 

k\= Intrinsic permeability with air, cm. 2 

L= Length of soil column, cm. 

V= Volume of tank, cm. 3 

7] = Viscosity of ai r at the temperature at which the 

determination was made, dyne sec. cm. -2 

(poises) . 
A = Cross-sectional area of sample, cm. 2 
P a = Atmospheric pressure, dynes/cm. 2 
5= Slope of log y vs. time curve= 

togioyi~logioy2 
At 
y ^Displacement of the water surface in one arm 

of the manometer, cm. 
A£=Time interval in seconds for the water sur- 
face in the manometer to drop from yitoy 2 . 

The time for a convenient and measurable drop in 
manometer level can be controlled by the volume of the 
tank used. For most soils prepared as outlined above, a 
213-liter (55-gal.) drum gives a convenient time inter- 
val for a measurable manometer change. For soils of 
lower permeability, a 24-liter tank is used. 

While c. g. s. units are suggested above, any con- 
sistent set of units can be used. 



Kirkham(1947), Soil Science Society of America 
(1952). 

(37b) Permeability of Soil to Water 

Apparatus 

Constant-level water-supply reservoir, glass siphon 
tubes, and rack for supporting samples; soil containers 
made from 3-oz. tinned iron soil cans with % 2 -inch hole 
punched in bottom and brass cylinder extensions, 
4-cm. high; 50- orlOO-ml. graduates. 

Procedure 

The procedure for preparing and packing samples is 
as outlined in Method 37a. Water-permeability deter- 
minations may be made on the same samples used for 
air permeability. Care must be exercised to avoid dis- 
turbance of the sample in handling. 

Following the air-permeability determination, place a 
brass cylinder extension on top of the can containing 
the soil sample and seal in place with an elastic band or 
beeswax. Place the soil sample on the rack, cover the 
soil surface with filter paper, and admit water to the 
samplefromthesupply reservoir with thesiphon. The 
water level is adjusted so that the height of soil plus 
water column is 2 times the soil column, giving a 
hydraulic gradient of 2. 

Record the water temperature, the time at which 
water is admitted to the container, and the time at 
which water first percolates through the sample. Meas- 



ure the volume of percolate for a number of successive 
time intervals. The amount of water passed through 
the soil and the number of volume measurements made 
will depend upon the purpose of the determination. 
Usually 3 to 6 in. is used, a depth corresponding to an 
irrigation. For comparing one soil with another and 
for determining the effect of various treatments on a 
given soil, use a value obtained after the hydraulic 
conductivity has become more or less constant. 

Calculations 

Intrinsic permeability of the soil using water is given 
by the equation: 

VL 



fc w 



- V L- 



V 



d^g dwg AAhAt 

in which 

A' w = Intrinsic permeability with water, cm. 2 
k-Hydraulic conductivity, cm./sec. 
V~ Volume of percolate in time, At, cm." 
L = Length of soil column, cm. 
Ah= Difference in hydraulic head between the in- 
flow and outflow ends of the soil column, 
cm. 
A= Cross-sectional area of the soil column, cm. 2 
At=Time interval for volume of percolate V to 

pass through the soil, sec. 
7j~ Viscosity of water at the recorded tempera- 
ture, dyne sec. cm. -2 (poises). 
d w ^= Density of water, gm./cm. 3 
g= Acceleration of gravity, cm. sec -2 

Intrinsic permeability is related to hydraulic conduc- 
tivity as indicated by the above equation. If desired, 
hydraulic conductivity may first be calculated and then 
converted to intrinsic permeability by multiplying by 
the ratio rj/d w g. While c. g. s. units are suggested 
above, any consistent set of units can be used. 

Remarks 

Soils may be compared with respect to permeability 
on the basis of values obtained at a fixed time after 
wetting or after a specified amount of water has passed 
through the sample. For comparing changes in struc- 
ture between different soils, the time basis has been 
found to be preferable. 



Soil Science Society of America (1952) . 

(38) Bulk Density 

Apparatus 

Balance, drying oven, moisture, boxes, and core sam- 
pler. The latter can be anything from an elaborate 
power-driven machine to a short section of thin-walled 
brass tubing with an internal closely fitting ring of 
clock spring soldered in place to form the cutting lip. 
(See drawing of soil sampler in Appendix.) 



259525 O - 54 - 9 



122 



AGRICULTURE HANDBOOK 60, U. S. DEPT. OF AGRICULTURE 



Procedure 

Details of procedure will, depend on the type of core 
sampler and soil conditions. Usually a flat soil sur- 
face, either horizontal or vertical, is prepared at the 
desired depth, and the core sampler is pressed or driven 
into the soil. Care should betaken to see that no com- 
paction occurs during the process, so that a known 
volume of soil having field structure is obtained. The 
oven-dry weight of the sample is then determined. 

Calculations 

Bulk density (rf b )= (wt. of oven-dry soil core) / (field 
volume of sample). Bulk density is expressed as 
pounds per cubic foot or grams per cubic centimeter. 
For practical purposes, the latter is equal numerically 
to apparent specific gravity or volume weight. 

(39) Particle Density 
Apparatus 

Balance, vacuum desiccator, and pycnometers. 
Procedure 

Weigh a pycnometer when filled with air ( W & ), 
when filled with water (JF W )> when partially filled with 
an oven-dried sample of soil (W,), and when com- 
pletely filled with soil and water (JT SW ). To exclude 
air, pycnometers containing the soil with enough water 
to cover should be subjected to several pressure reduc- 
tions in a vacuum desiccator and then allowed to stand 
for a number of hours under reduced pressure before 
completely filling with water for weighing W sw . The 
particle density (d,) of the soil in gm. cm. -3 , is then 
given by the formula : 

d p = d w (W B -W*)/(W* + W*-W % -W„) 

whered w is the density of the water in gm.cm." 3 . 

Slightly different and perhaps better vaiues will be 
obtained for d p if a nonpolar liquid such as kerosene, 
xylene, or acetylene tetrachloride is used for the dis- 
placing liquid. 

(40) Porosity 

The porosity of soil is the fraction of the soil space 
not occupied by soil particles. The porosity (n) may 
be calculated from the formula: 

n=(c?p — d h ) /d v 

if the bulk density (d h ) and the particle density (d,) 
are known. Solutions of this equation may be found 
graphically by use of the nomograms given at the right 
of figure 8 (ch. 2). 

(41) Particle-Size Distribution 

Remarks 

The method as given is essentially that described by 
Kilmer and Alexander (1949), except that the 0.005- 



mm. determination has been omitted. The names used 
at present by the United States Department of Agricul- 
ture for the soil separates are as follows: The diameters 
2.0 to 1.0, 1.0 to 0.5, 0.5 to 0.25, 0.25 to 0.1, and 0.1 to 
0.05 mm., respectively, separate very coarse, coarse, 
medium, fine, and very fine sands; particles from 0.050 
to 0.002 mm. are called silt, and particles with effective 
diameters less than 0.002 mm. are designated as clay. 
With the International System, the diameters 2. , 0.2, 
and 0.02, respectively, separate the classes represented 
by the numerals 1,11, and III, while particles of diam- 
eters less than 0.002 mm. are represented by IV. 

Apparatus 

Set of sieves; size openings, 2-, I-, and 0.5.mm. round 
hole; 60-, SO-, 140-, and 300-mesh per in. Pyrex nurs- 
ing bottles, 8-oz., with rubber stoppers; Lowy 25-ml. 
automatic pipet; haw pipet rack; Pasteur-Chamberland 
filters, short, "F" fineness. Analytical balance, drying 
oven, steam chest, motor stirrer, reciprocating shaker, 
desiccator, beakers, and evaporating dishes. 

Reagents 

A. Hydrogen peroxide, 30 percent solution. 

B. Dispersing agent. Dissolve 35.7 gm. sodium 
metaphosphate and 7.94 gm. sodium carbonate in water 
and dilute to 1 liter. The sodium metaphosphate is 
prepared as follows: 125 gm. of monosodium phos- 
phate (NaH 2 P0 4 *H 2 0) is slowly heated in a platinum 
dish to 650" C. This temperature is held for l 1 /^ hr. 
The platinum dish and its contents are removed from 
the furnace and the sodium metaphosphate is cooled 
rapidly by pouring it out in narrow strips on a clean 
marble slab. The sodium carbonate is used as an 
alkaline buffer to prevent the hydrolysis of the meta- 
phosphate back to the orthophosphate which occurs in 
acidic solutions. 

Procedure 

General statement. — Samples are routinely run in 
sets of eight; the necessary equipment is designed 
accordingly. The sample is treated with hydrogen 
peroxide, washed, filtered, and dispersed. The sand is 
separated from the silt and clay by washing the dis- 
persed sample through a 300-mesh sieve. The various 
sand fractions are obtained by sieving, while the 
20-fi and 2-ju fractions are obtained by pipeting. 
Organic matter is determined on a separate sample by 
the dichromate reduction method (Peech and co- 
workers, 1947). 

Preparation of the sample. — The air-dried sample 
is mixed and quartered. The quarter reserved for 
analysis is rolled with a wooden rolling pin to break 
up the clods. The sample is then passed through a 
sieve with 2-mm. round holes. Rolling and sieving of 
the coarse material are repeated until only pebbles are 
retained on the sieve. The material not passing the 
sieve is weighed and reported as a percentage of the 
air-dry weight of the whole sample. 



SALINE AND ALKALI SOILS 



123 



Removal of organic matter.-A 10-gm. sample 
of the air-dry soil containing no particles larger than 
2 mm. is weighed on a rough balance and placed in a 
250-ml. electrolytic Pyrex beaker. About 50 ml. of 
water is added, followed by a few milliliters of 30 per- 
cent hydrogen peroxide. The beaker is then covered 
with a watch glass. If a violent reaction occurs, the 
cold hydrogen peroxide treatment is repeated period- 
ically until no-more frothing occurs. The beaker is 
then heated to about 90" C. on an electric hot plate. 
Hydrogen peroxide is added in 5-ml. quantities at 
about 45-min. intervals until the organic matter is 
essentially removed as determined by visual inspection. 
Heating is then continued for about 30 min. to remove 
any excess hydrogen peroxide. 

Removal of dissolved mineral matter. — Follow- 
ing the hydrogen peroxide treatment, the beaker is 
placed in a rack and about 150 ml. of water is added 
by means of a jet strong enough to stir the sample 
well. The suspension is filtered by means of a short 
Pasteur-Chamberland filter of "F" fineness. Five such 
washings and filterings are usually sufficient except 
for soils containing much coarse gypsum. Soil adher- 
ing to the filter is removed by applying a gentle back- 
pressure and using the forefinger as a policeman. The 
beaker is then dried on a steam bath, placed overnight 
in an oven at 110" C, cooled in a desiccator, and then 
weighed to the nearest milligram. After the sample is 
transferred to a nursing bottle for dispersion, the oven- 
dry weight of the beaker is obtained. Weight of 
oven-dry organic-free sample is used as the base weight 
for calculating percentages of the various fractions. 

Dispersion of the sample. -To the oven-dry 
sample is added 10 ml. of sodium hexametaphosphate 
dispersing reagent B, and the sample is transferred to an 
8-oz. Pyrex glass nursing bottle by means of a funnel, 
a rubber policeman, and a jet of water. The volume 
is made to 6 oz., and the bottle is stoppered and 
shaken overnight on a horizontal reciprocating shaker 
with 120 oscillations per minute. A similar volume of 
dispersing agent is placed in a I iter cylinder, the volume 
made to 1,000 ml. and well mixed. A sample is taken 
with thepipet, dried, and weighed to obtain the weight 
correction referred to in the section on calculations. 
This weight correction is obtained for each new solu- 
tion of sodium metaphosphate. 

Separation of the sands from silt and clay.- 
The dispersed sample is washed on a 300-mesh sieve, 
the silt and clay passing through the sieve into a 1-liter 
graduated cylinder. The sieve is held above the 
cylinder by means of a clamp and a stand. Jets of 
water should be avoided in washing the sample. The 
sieve clamp is tapped gently with the side of the hand 
to facilitate the washing procedure. Washing is con- 
tinued until the volume in the cylinder totals about 800 
ml. The sands and some coarse silt remain on the 
sieve. It is necessary that all particles of less than 
20/jt diam. be washed through the sieve. The sieve 
is removed from the holder, placed in an aluminum 
pan, and dried at 110" to 120" C. While the sands are 



drying, another sieve is used for the next sample. The 
material on the sieve is then brushed into a platinum 
dish and further dried for about 2 hr. The dish is then 
placed in a desiccator, the contents to be sieved and 
weighed when convenient. The silt and clay suspen- 
sion in the cylinder is made up to 1 liter with distilled 
water, covered with a watchglass, and set aside until the 
pipetings are to be made. 

Pipeting. — Pipetings are made for the 20/x and 2/* 
particles in the order named. The 20/x particles are 
pipeted at a 10-cm. depth, the sedimentation time vary- 
ing according to the temperature. The 2/* fraction is 
pipeted after a predetermined settling time (usually 
6 to 6y 2 hr.), the depth varying according to the time 
and temperature. A Lowy 25-ml. automatic pipet with 
a filling time of about 12 sec. is used. Prior to each 
sedimentation process, the material in the sedimentation 
cylinder is stirred for 6 min. with a motor-driven stirrer 
(8 min. if the suspension has stood for more than 16 
hr.). After removal from the stirrer, the sedimenta- 
tion cylinder is surrounded with insulating material 
and the suspension is stirred for 30 to 60 sec. with a 
hand stirrer, an up-and-down motion being used. This 
stirrer is made by fastening a circular piece of per- 
forated brass sheeting to one end of a brass rod. A 
wide rubber band is placed around the edge of the brass 
sheeting to prevent abrasion. The time is noted at com- 
pletion of the stirring. About 1 min. before the sedi- 
mentation is complete, the tip of the 25-ml. pipet is 
lowered slowly into the suspension to the proper depth 
by means of a Shaw pipet rack. Thepipet is then filled 
and emptied into a 60-ml. weighing bottle having an 
outside cover. One rinse from the pipet is added. A 
vacuum is used to dry the pipet for use on the next 
sample. The weighing bottle is dried in an oven at 95" 
to 98" C. and then further dried for about 4 hr. at 
110". The initial drying is done at a lower tempera- 
ture to prevent spattering of the suspension. The 
weighing bottle is then cooled in a desiccator contain- 
ing phosphorus pentoxide as a desiccant and weighed. 

Seving and weighing the sand FRACTIONS.-The 
dry sands, including some coarse silt, are weighed and 
brushed into a nest of sieves. Sieves and specifications 
are as follows: 

Sieve Opening Specifications 

(mm.) 

1.0 Perforated brass plate, round holes, No. 

3 straight, 0.04-in. diam. holes, 240 
holes per in. 2 

0.5 Perforated brass plate, round holes, No. 

00 staggered, 0.02-in. diam. holes, 
714 holes per in. 2 

0.25 60-mesh, Bureau of Standards (Phos- 
phor Bronze wire cloth) 

0.177 80-mesh, Bureau of Standards (Phos- 
phor Bronze wire cloth) 

0.105 140-mesh, Bureau of Standards (Phos- 
phor Bronze wire cloth) 

0.047 300-mesh (Phosphor Bronze wire 

cloth), 0.0015-in. wire. 



124 



AGRICULTURE HANDBOOK 60, U. S. DEPT. OF AGRICULTURE 



(An 80-mesh sieve is included in order to obtain 
International Society of Soil Sciences fraction I.) The 
sands are then shaken for 3 mi n. on a shaker having 
vertical and lateral movements of y 2 in., making 500 
oscillations per minute. For a different shaker, the 
time of shaking would have to be determined by 
microscopic study. The summation method of weigh- 
ing is used. The first sand fraction is weighed, the 
second fraction added to it, the total weight determined, 
and so on. If the sum of the weights of the fractions 
is equal to the total weight, it is assumed that no weigh- 
ing error has been made. 

Calculations 

Pipeted fractions. — ( A — B ) KD = percent of pi- 
peted fraction where A = weight in gm. of pipeted frac- 
tion, B-weight correction for dispersing agent in gm.) , 



K= 



1,000 



and 

D= 



volume contained by pipet 
100 



organic-free oven-dry weight of total sample 



(The 1 20/x fraction) — (the 2\k fraction) = Interna- 
tional Society of Soil Sciences fraction III. United 
States Department of Agriculture silt is obtained by 
subtracting the sum of the percentages of sand and 
clay from 100. International Society of Soil Sciences 
fraction II is obtained by subtracting the sum of the 
percentages of fractions I, III, and IV from 100. 

SAND FRACTIONS. — 



(Weight in grams of fraction on sieve X 100) 
(organic-free oven-dry weight of total sample) 
percent of fraction 



Kilmer and Alexander (1949),Peech and others 
(1947), and Tyner (1940). 

(42) Aggregate-Size Distribution 

(42a) Wet Sieving 

Remarks 

This is a modification of the mimeographed tentative 
method that was distributed in August 1951 by the 
Committee on Physical Analyses of the Soil Science 
Society of America. The method in brief consists of 
placing a sample of soil on a nest of sieves that is 
oscillated vertically under water. The amount of soil 
remaining on the individual screens is determined, and 
aggregation is expressed as the mean weight-diameter 
of the aggregates and primary particles. After weigh- 
ing, the aggregate separates are combined and dis- 
persed and washed through the nest of sieves. The 



resulting separates make it possible to correct the pre- 
vious separates of aggregates for primary particles and 
to calculate the aggregation index. This is a single- 
value index of the aggregation of a soil. 

Apparatus 

Yoder-type wet-sieving apparatus, sieve holders, 4 
sets of 5-inch sieves with 2-,l-,0.5-,0.25-, and O.IO-mm. 
openings (corresponding to United States Screens Nos. 
10, 18, 35, 60, and 140), drying oven, moisture cans, 
balance Pyrex watchglasses, and 6-in. diameter porce- 
lain funnel. 

Procedure 

Collect the soil sample with spade or garden trowel, 
preferably when the soil is moist, avoiding excessive 
compaction or fragmentation of soil. Dry the sample 
slowly and, when sufficiently friable, pass it gently 
through an S-mm. sieve and air-dry. If the soil is 
stony, pass the sample through a 4-mm. sieve and dis- 
card all primary material greater than 4 mm. in size. 
Mix the soil and take subsamples in accordance with 
Method 1. Make determinations in duplicate on 40- to 
60-gm. subsamples. Weigh the subsamples to the 
closest 0.1 gm. and determine the moisture content by 
drying a separate subsample at 105" C. 

Install the nests of sieves in the water slowly and at 
a moderate angle to avoid entrapping air bubbles below 
the sieves. Adjust the mechanism so that the top sieve 
makes contact with the water surface when the oscilla- 
tion mechanism is at the top of its stroke. Distribute 
the sample on the top sieve so that wetting occurs by 
capillarity and wait 5 to 10 min. after the soil surface 
appears wet to insure saturation of the aggregates. 
Oscillate the sieves for 30 min. with a stroke of 3.8 cm. 
and a frequency of 30 cycles per minute, keeping soil 
submerged at all times. Some attention may be re- 
quired during the first few minutes of operation, in 
order to prevent water from spilling over the top sieve, 
and later, to prevent the top sieve from rising above 
water level. 

Remove the sieves from the water and drain for a few 
minutes in an inclined position. Remove excess water 
from the bottom of the screens with absorbent tissue 
and place the sieves on watchglasses. Dry in a circu- 
lating oven at not higher than 75" C. because high 
temperatures cause some soils to adhere. Then remove 
the soil from the sieves, dry at 105°, and weigh. 

In order to determine how much of the soil retained 
on the individual sieves represents aggregates and how 
much is gravel and sand, the oven-dried soil taken from 
the five sieves is dispersed and washed through the 
sieves with a stream of water. The oven-dry weight of 
the primary particles remaining on each sieve is then 
determined. 

Calculations 

The amount of soil remaining on each sieve is ex- 
pressed as percentage of the total sample. Prepare a 



SALINE AND ALKALI SOILS 



125 



graph, plotting the accumulated percentage of soil 
remaining on each sieve as ordinate against the upper 
limit of each fraction in millimeters as the abscissa, 
and measure the area shown by the curve connecting 
these points and by the ordinate and the abscissa. If 
1 mm. (sieve size) represents 1 unit of the abscissa and 
10 percent a unit on the ordinate, a square unit will 
represent 0.1 mm. mean weight-diameter of the aggre- 
gates of the sample. Multiplying the number of square 
units of the area by 0.1 gives the mean weight-diameter 
of the entire sample, including the material that has 
been washed through the smallest sieve. 

The results from the wet sieving of the dispersed 
sample are plotted and calculated in the same way. 
The difference between the mean weight-diameters of 
the original and the dispersed samples gives the aggre- 
gation index. 

Remarks 

The water container in which the sieve nest is oscil- 
lated can be of any desired size or shape, providing 
its area is at least 1.6 times the area of the sieves. The 
temperature of the water should be in the range 20" 
to 24" C, and the water should not be excessively 
saline. Fresh water should be used for each set of 
determinations. Rubber bands cut from old inner 
tubes are convenient for holding loosely fitting sieves 
together. 

References 

Russell (1949), Van Bavel (1950). 

(42b) Aggregation of Particles Less than 
50 Microns 

Remarks 

This procedure measures the degree of aggregation 
of the silt and clay (less than 50/x) fraction for those 
soils that do not contain enough large aggregates to be 
adequately characterized by wet-sieving. The method 
involves measuring the concentration of two suspen- 
sions of the same soil, one of which is dispersed by 
any standard dispersion procedure to give total silt 
plus clay. The other suspension, prepared by mild 
(end-over-end) agitation of the sample in water, gives 
a measure of the unaggregated silt plus clay. The 
difference in concentration between the two suspensions 
provides a measure of the amount of silt plus clay 
particles thzt is bound into water-stable aggregates 
larger than 50/x in size. 

This procedure may also be used as a rapid ex- 
ploratory test to determine the effect of various soil- 
aggregating chemicals in producing water-stable 
aggregation. 

Apparatus 

Dispersion apparatus with high-speed stirring motor: 
metal cup, I -I iter hydrometer jars, thermometer, and 



Bouyoucos hydrometer or hydrometer-pi pet. If the 
pipet procedure is used, a Lowy automatic pipet, a 
Shaw pipet rack, and tared moisture boxes are needed. 

Procedure 

Weigh two 50-gm. subsamples of air-dried soil 
prepared as in Method 42a. Make a moisture de- 
termination on a separate subsample. 

Total silt plus clay. — Disperse one of the sub- 
samples in the dispersion apparatus. Transfer to a 
hydrometer jar and dilute with distilled water to the 
required volume. For procedure a (below) the final 
volume is 1,130 ml., determined with the hydrometer 
in the suspension; for procedures b and c, the volume 
is 1,000 ml. (Note: If either procedure b or c is to be 
used, stopper and invert the cylinder 2 or 3 times and 
record the temperature. This is necessary in order to 
determine in advance the settling time used.) 
Stopper, invert, and shake the cylinder vigorously sev- 
eral times and determine the total silt plus clay in the 
suspension as directed under procedures a, b, or c, given 
below. 

Unbound silt plus CLAY.-lncline the hydrometer 
jar containing the second subsample to a nearly hori- 
zontal position and shake lightly to spread the sample 
over a distance of 10 or 12 cm. along the side of the jar. 
Add distilled water slowly and in such manner as to 
favor wetting by capillarity rather than by flooding. 
When soil is completely wetted, dilute to the appropri- 
ate volume, as given above, but do not allow water to 
fall directly on soil. Allow the soil to slake for at least 
15 mi n. Record the temperature. Stopper the cyl i nder 
and gently invert it 20 times (do not shake) within a 
period of about 40 sec., requiring about 1 sec. for 
inversion with a 1-sec. interval between inversions. 
After the required settling period, determine the amount 
of unbound silt plus clay in suspension by the same 
procedure a, b, or c used for the total silt plus clay 
measurement. 

Procedures for measuring concentration of SUS- 
PENSIONS.- {3) Hydrometer. After final mixing, in- 
sert the hydrometer and take a reading after 40 sec- 
onds, as prescribed by Bouyoucos (1936). Immedi- 
ately record the suspension temperature in degrees F. 
and apply a temperature correction as follows: Add 
0.2 to the hydrometer reading for each degree above 
67" F.; subtract if below. 

The corrected hydrometer reading gives the grams 
per liter of silt plus clay in suspension. 

(b) Hydrometer-pipet. The hydrometer-pi pet (Hell- 
man and McKelvey, 1941) measures the concentration 
of soil particles in grams per liter of a suspension that 
has. been pipeted from a known depth and that is uni- 
form throughout when measured by the hydrometer 
contained within the pipet. The settling time and 
depth of sampling are the same as for the pipet pro- 
cedure c, and the hydrometer readings require the same 
temperature corrections as for the hydrometer pro- 
cedure a. 



126 



AGRICULTURE HANDBOOK 60, U. S. DEPT. OF AGRICULTURE 



After final mixing and a few seconds prior to time 
of sampling, squeeze the bulb and insert the hydrometer- 
pipet into the suspension to a depth of 12.5 cm. Start 
filling the pipet after the prescribed time interval in 
seconds', as indicated under procedure c. Careshould 
be taken to keep the suspension well mixed by occa- 
sionally allowing a bubble to rise through the suspen- 
sion in the pipet. Read the hydrometer at the top 
of the meniscus and apply the proper temperature cor- 
rection as prescribed for the Buoyoucos hydrometer. 

The corrected hydrometer-pi pet reading gives the 
grams per liter of silt plus clay in suspension. 

(c) Pipet. After final mixing, insert the Lowy or 
other suitable pipet into the suspension to a depth of 
12.5 cm. Start filling the pipet after the time-interval 
in seconds indicated by the accompanying data. Other 
depth-time-temperature relationships may be obtained 
from the nomograms of Tanner and Jackson (1948). 



Temperature 



'C. or "F. 



20 
22 
24 
26 
28 
30 



(68)- 

(71.5) 
(75)__ 
(79)-. 
(82.5) 
(86) „ 



Time to sample at 

12.5-cm. depth 

(seconds) 



57 
54 
51 
49 
46 
44 



The weight in grams of oven-dry (105" C.) material 
in the25-ml. aliquot is multiplied by 40 to give grams 
per liter of silt plus clay in suspension. 

Calculations 

Percent aggregation = (wt. of total silt plus clay in 
dispersed suspension, gm., minus wt. of silt plus clay in 
undispersed suspension, gm.) X 100/ ( wt. of total silt 
plus clay in dispersed suspension, gm.) - 



Bouyoucos (1936),Hellman and McKelvey(1941), 
and Tanner and Jackson (1948). 

(43) Modulus of Rupture 
Remarks 

In the following procedure, the maximum force re- 
quired to break a small specially molded briquet of 
soil is measured, and from this breaking force the maxi- 
mum fiber stress in the standard sample is calculated. 

Shrinkage of soil material on drying is a pertinent 
property and can be determined from the dimensions 
before and after drying of the briquet samples used 
in thistest. 

Apparatus 

The machine for breaking the sample makes use of 2 
parallel bars 5 cm. apart for supporting the sample. 
The breaking force is supplied from a third overlying 
bar centrally located and parallel with respect to the 
supporting bars. The bar above and one bar below are 



self-alining to accommodate to any slight lack of paral- 
lelism in the line of bearing on the sample. The bars 
are coated with a strip of soft rubber with a cross sec- 
tion 0.16 cm. square. The breaking machine is mounted 
on the platform of a beam balance. The briquet sample 
is broken by upward motion of the two lower bars, 
which are supported by the platform of the balance. 
Upward motion of the upper bar is constrained by a 
cross frame above the balance. The breaking force is 
supplied by water accumulating in a vessel hung from 
the end of the balance beam. The breaking force is 
applied at the rate of 2,000 gm.-wt./min., and-the beam 
motion that occurs when the sample breaks can be used 
to automatically stop the accumulation of water in the 
vessels. 

The briquet molds are precision made from %-in, 
brass strip-with inside dimensions of Sy 2 cm. by 7 cm. 
by 0.952 cm. high. Rectangles of hard white photo- 
graphic blotting paper are cut to the size 5 cm. by 
8V^> cm. A screen-bottomed tray, 50 cm. square, is 
made by pulling brass window screen taut and solder- 
ing it to a rigid % -in. galvanized pipe frame. A pan 
or other water container slightly larger than 50 cm. 
square. Graduated cylinder. Tremie funnel with 
straight cylindrical tube 2 cm. diam. and 10 cm. high. 
(See drawing of apparatus in Appendix.) 

Procedure 

Make the determination on 6 replicate samples of 
soil that have been passed through a 2-mm. round-hole 
sieve, using the subsampling procedure outlined in 
Method 1. Samples should be just slightly larger than 
will fill the briquet molds. Cover the inside of the 
molds with a thin layer of Vaseline so that the soil will 
not stick to the mold. Place the screen-bottomed tray 
in the pan. PI ace the molds on the blotting paper on 
the screen . Rest the tremi e on the bl otti ng paper at one 
end of themold. Dump all of a soil subsample into the 
tremie. Move the funnel around inside the mold while 
raising continuously so as to give a uniform smooth 
filling of the mold. 

Strike off excess soil level with the upper surface of 
the mold. Add water to the pan until free water sur- 
rounds every mold. Allow samples to stand for 1 hour 
after all the soil samples become wet. Raise the screen 
very carefully so as not to jar the samples and transfer 
to a forced -draft oven at 50" C. After drying the 
briquets to constant weight, remove from the molds and 
determine the breaking strength. 

Calculations 

Use the formula s=(3FL)/ (2bd 2 ), where 5 is the 
modulus of rupture (in dynes per sq. cm.), F is the 
breaking force in dynes (the breaking force in 
gm.-wt. x 980) ; L is the distance between the lower two 
supporting bars, b is the width of the briquet, and d is 
the depth or thickness of the briquet, all expressed 
in cm. 



Chapter 7 



Methods of Plant Culture and Plant Analysis 



Plant-Culture Techniques Adapted to Salt- 
Tolerance Investigations 

There are certain aspects of salt-tolerance investiga- 
tions involving extensive plant breeding and selection 
programs that are being conducted by crop specialists 
at a number of agricultural experiment stations. 
Furthermore, since salt tolerance of plants may be in- 
fluenced profoundly by climatic conditions, investiga- 
tors in a given region may find it desirable to under- 
take salt-tolerance studies under local climatic condi- 
tions in order to determine the crops best suited to 
their region. In anticipation of a continued interest 
in such breeding and testing programs, techniques used 
in such studies at the Salinity Laboratory are included 
in this handbook. 

(50) Artificially Salinized Field Plots 

Information is needed regarding the response of crop 
plants to adverse saline conditions as related to cli- 
matic factors, planting techniques, and cultural prac- 
tices used in the field. However, field observations 
relating crop growth to the salinity of the soil are 
difficult to evaluate, because of the wide range of salt 
concentrations frequently encountered within a small 
area in the field. In order to obtain information on 
these aspects of salt tolerance, an artificially salinized 
field-plot technique may be employed (Wadleigh and 
Fireman, 1949). Small, 14-ft. square plots are used, 
and each crop is managed according to practices gen- 
erally followed in the principal regions where it is 
grown under irrigation. Density of stand, spacing, 
fertilizer practice, irrigation methods, and other con- 
ditions are all reproduced as closely as possible. The 
salt tolerance of field, vegetables, forage, and tree crops 
may be studied by this technique. 

In the preparation of plots, careful leveling is neces- 
sary to insure uniform distribution and penetration of 
the salinizing water, and all parts of a basin-irrigated 
plot should be brought to within *4 in- of the mean 
plot level. Similar precautions should be used where 
furrow irrigation is to be practiced so that all bed 
surfaces and furrows will be at uniform levels. The 
salinizing waters can be restricted to the plots by 
borders; and, if the plots are closely spaced, the borders 
can be supplemented with 6-in. boards around the plot. 
Asphalt roofing paper 18 in. wide can be attached to 



the boards and buried to a 12-in. depth. If the soil 
is sufficiently permeable and adequate irrigations are 
applied, salt concentration in the plot tends to reach a 
steady value following the first several irrigations with 
a minimum of variability within the plot. 

In order to avoid the development of alkali condi- 
tions in the soil, it has been standard practice to add 
salts to the irrigation water as equal parts of sodium 
chloride and calcium chloride. This is readily accom- 
plished for small plots by dissolving the desired amount 
of salts in water in a galvanized tank and mixing with 
the aid of a circulating pump. Salinity levels com- 
monly employed in salt-tolerance tests are 0, 3,000, 
6,000, and 9,000 p. p. m. of added salts, although a 
more dilute series may be desirable for the more salt- 
sensitive crops, such as beans and fruit trees; and a 
more concentrated series for salt-tolerant crops, such 
as barley and beets. Salinization of the plots is begun 
after the seedlings or transplants are established be- 
cause of the greater sensitivity of most crops to salinity 
during germination and immediately following trans- 
planting. To avoid the shock, which too abrupt a 
change in soil salinity may induce in the plant, it is 
advisable to increase salinity stepwise during the first 
3 or 4 salinizing irrigations. By applying relatively 
light irrigations at frequent intervals, the salinization 
of a series of plots may be completed in 7 to 10 days. 
However, owing to dilution of the salinizing water by 
residual soil moisture, a few additional salinizing irri- 
gations may be required to establish a relatively con- 
stant concentration of salt in the plot. 

Subsequent irrigations are usually applied at con- 
ventional frequencies, as judged by the condition of 
the control plot. The salt status of the salinized plots 
is determined periodically during the growth of the 
crop by taking soil samples at various depths in the 
beds and furrows and determining the conductivity of 
the saturation extract (EC?). Yield data and observa- 
tions on crop quality and composition can then be 
correlated with the salt status of the several plots in the 
series. 

Plots treated in the above manner may be reused 
after leaching the salt from the soil. Although the plots 
remain nonalkali, recovery is facilitated by the addi- 
tion of gypsum at the rate of 1 ton per acre. To insure 
continued uniformity of the plots with regard to soil 
structure (as measured by water penetration, aeration, 
and other properties) , it is desirable to grow some salt- 

127 



128 



AGRICULTURE HANDBOOK 60, U. S. DEPT. OF AGRICULTURE 



tolerant grass following leaching and prior to reusing 
the plots. 

The above procedure may be modified for certain 
purposes. For crops that may be specifically sensitive 
to high concentrations of soluble calcium or chloride, 
the composition of the added salt may be changed to 
vary the sodium: calcium ratio, or sulfate may be sub- 
stituted for some or all of the chloride. The solubility 
of calcium sulfate is a limiting factor in making such 
substitutions, and the effect of high ratios of sodium 
to calcium on the exchangeable-sodium-percentage must 
be taken into account. 

Inasmuch as this procedure does not include observa- 
tions on the salt tolerance of the crop during germina- 
tion, this must be determined separately, either by a 
laboratory technique (Ayers and Hay ward, 1949) or 
by a modification of the artificially salinized field-plot 
technique. The plots may be salinized prior to plant- 
ing with a series of waters of graded concentrations. 
Salinity levels are then determined by EC e measure- 
ments, and the seeds are planted according to standard 
or experimental practice. Irrigating with water, 
usually much less saline than that used in salinizing 
the plots, will result in a redistribution of salt, espe- 
cially where furrow irrigation is practiced. Germina- 
tion counts will serve to delimit the critical level of 
salinity which can be tolerated by the crop at the time 
of planting under the specific cultural conditions 
employed. 

(51) Drum Cultures 

Drum cultures have been used extensively for studies 
of salt tolerance relating to the specific effects of various 
added salts and to the frequency of irrigation as it 
interacts with salinity in affecting the growth of plants 
(Wadleigh and coworkers, 1951; Wadleigh and Ayers, 
1945) . Since the number of treatments may be greatly 
increased with a minimum of space and effort by using 
drum cultures, this technique has a very definite place 
in salinity investigations. 

Salinization of drum cultures requires a different 
technique from that employed with artificially salinized 
plots. Any salt added to the drums remains in the soil 
and is not moved downward past the root zone by subse- 
quent irrigations as in field plots. It is, therefore, 
necessary to add the salt only in the initial irrigation 
of the drums or by mixing salt with the dry soil in 
amounts calculated to give the desired salinity levels. 
Thereafter, nonsaline water must be used in irrigating 
to avoid further increases in the salt concentration of 
the soil. However, repeated irrigations with nonsaline 
water will tend to leach the salt downward in the drum, 
and a very steep gradient in salt concentration will 
ensue. 

In order to maintain a relatively uniform distribu- 
tion of salt in the soil, it is necessary to irrigate alter- 
nately on the surface and by subirrigation. For sub- 
irrigation, provision is made for introducing the 
irrigation water into a layer of fine gravel in the bottom 



of the drum before filling with soil. With alternate 
surface and subirrigation the distribution of the salt 
in the soil can be maintained more nearly uniform. 
Frequency of irrigation may be determined by daily 
weighings of the drum cultures and calculation of mean 
soil-moisture content. It is important to avoid over- 
irrigation of the drums, since drainage, if permitted, 
will result in loss of salt; or, if drainage is prevented, 
the saturated soil condition will inhibit proper root 
activity. 

( 52 ) Sand and Water Cultures 

Frequently, problems difficult to solve by soil-culture 
methods can be studied more satisfactorily by sand or 
water cultures, because the latter allow for a more pre- 
cise control of the substrate. Salinity studies using sand 
or water cultures involve the addition of various salts 
to a base nutrient solution. The salts may be added in 
isosmotic concentration to facilitate comparisons of 
growth or in isoequivalent concentration to permit a 
readier comparison of accumulation of the elements in 
question. Occasionally, the two methods of adjusting 
salt concentration are combined to permit both 
isosmotic and isoequivalent comparisons, or a series of 
concentrations of each salt may be used, and the effect 
of osmotic pressure and equivalent concentration de- 
termined by graphical analysis of the data. By these 
techniques the effects of various ions, such as sodium, 
potassium, calcium, magnesium, chloride, sulfate, and 
bicarbonate, on the growth and composition of plants 
may be studied. In sand or water cultures the treat- 
ments are not altered as a result of cation exchange, 
nor is fluctuating moisture content a disturbing factor 
as it is in soil cultures. 

For sand and water cultures, provision must be made 
for adequate nutrition by use of a base nutrient solu- 
tion, proper control of the pH of the nutrient solution, 
and adequate aeration. 

Methods of Plant Analysis 

[See the introductory notes at the beginning of chapter 6] 

(53) Sampling and Preparation of Plant 
Samples 

In collecting plant samples for chemical analysis in 
connection with salinity studies, the usual care should 
be practiced to obtain material representative of the 
plant population. Since plant organs may differ 
markedly in their selectivity in accumulating various 
ions, it is frequently desirable to collect separate frac- 
tions of the various plant parts: leaves, stems, and 
roots. In taking leaf samples it is the usual practice 
to select mature, fully expanded leaves, avoiding 
senescent ones, since salt accumulation may vary with 
age of leaf. If some leaves are affected by leaf burn 
or other visual symptoms of salt injury, separate 
samples of affected and normal leaves may furnish data 
of diagnostic importance. 



SALINE AND ALKALI SOILS 



129 



Remove surface contamination of the plant material 
by brushing and brief rinsing in distilled or deminer- 
alized water. If iron or other heavy metals are to be 
determined, rub the entire surface gently in 0.3 N 
hydrochloric acid and rinse. Dry the sample rapidly 
in a forced-draft oven at 70° C. Grind the sample in a 
Wiley mill, or by means of a mortar and pestle if 
metallic contamination is to be avoided. Mix well and 
store in tightly stoppered containers. Label each 
sample, giving information on species, plant part 
sampled, fresh weight, date, collector, and other 
pertinent data. 

If soluble sap constituents are to be determined, 
freeze weighed amounts of fresh plant material in wide- 
mouthed jars and store at —10° C. To obtain sap, 
thaw the plant material quickly by immersing the con- 
tainer in running water, press at 10,000 to 15,000 lb. 
per sq. in. until the major portion of the sap has been 
released. Centrifuge the liquid 15 min. at RCF= 1,500, 
pour off the supernatant liquid, and save for analysis. 
The expressed sap may be kept for several days in a 
refrigerator if a few drops of toluene are added, but 
analysis of the fresh sap is preferred. When the de- 
termination of insoluble constituents is desired, com- 
bine the residue from the centrifuge tube with the press 
cake, determine moisture content, and analyze for de- 
sired constituents. Correct these results on the basis 
of moisture content of the press cake and the concen- 
tration of soluble constituents of the sap. 

Procedures for chemical analyses of plant materials 
routinely employed in salt-tolerance studies are de- 
scribed under Methods 54 to 62. Additional determi- 
nations of various plant constituents are sometimes de- 
sirable, depending upon the specific problems under 
investigation. Methods employed in studies of bicar- 
bonate-induced chlorosis have been described by Wad- 
leigh and Brown (1952). 

(54) Ashing 

(54a) Wet Digestion 

This procedure is preferable to dry ignition, because 
of the possibility of loss of mineral constituents at high 
temperatures during dry ignition. 

Reagents 

A. Nitric acid, cone. 

B. Perchloric acid, 72 percent. 

Procedure 

Transfer 1.000 gm. of dried plant material or an 
equivalent volume of sap (usually 10 ml.) to a 50-ml. 
beaker and add 20 ml. of reagent A. Cover with a 
watchglass and allow to stand until initial reactions 
subside. Heat until solid particles have nearly dis- 
appeared, cool, add 10 ml. of B. Caution: Perchloric 
acid is explosive in presence of easily oxidizable organic 
matter. Heat gently at first, then heat more vigorously 
until a clear, colorless solution results. Do not take to 



dryness; discontinue heating when the volume is re- 
duced to approximately 3 ml. Cool and transfer quan- 
titatively to a 100-ml. volumetric flask, make to volume, 
mix, allow to stand overnight and filter through a dry 
filter paper without washing. Retain this solution and 
use for analyses as described under Methods 55 to 58 
and 61. 

Reference 

Toth and associates (1948). 

( 54b ) Magnesium IS Urate Ignition 

Since the wet-digestion procedure does not quanti- 
tatively retain sulfur, magnesium nitrate ignition should 
be used in the determination of sulfur in plants. Total 
phosphorus may be determined in the ignited material 
as well, since phosphorus is quantitatively oxidized to 
phosphate by this ignition. 

Reagents 

A. Magnesium nitrate solution. Add 113 gm. of 
magnesium oxide to 300 ml. of water and stir to a 
paste. Add nitric acid (1 + 1) until the magnesium 
oxide is in solution. Add a little excess magnesium 
oxide and boil; filter and dilute to 1 liter. 

B. Hydrochloric acid (1 + 1). 

Procedure 

Weigh 2.000 gm. of the sample and transfer into a 
large porcelain crucible or casserole. Add 10 ml. of 
reagent A, taking care that all the material is brought 
in contact with the solution, and heat gently on a hot 
plate to 180° C. until the reaction is complete. Trans- 
fer the crucible while hot to an electric muffle and 
allow to remain at low heat (muffle must not show any 
red) until the charge is thoroughly oxidized. No black 
particles should remain. (It may be necessary to break 
up the charge and return to the muffle.) Remove from 
the muffle and allow to cool. Moisten the ash with 
water and add 10 ml. of B, which should provide an 
excess of acid. Evaporate to dryness, moisten with B, 
and again evaporate to dryness to dehydrate silica. 
Add 5 ml. of B and sufficient water to bring the salts 
into solution. Allow to stand on the steam bath until 
solution is complete. Filter, wash, and make to 100 
ml. with water. Retain this solution for analysis of 
sulfur and phosphorus according to Methods 60 and 61. 

Reference 

Association of Official Agricultural Chemists (1950, 
2.8 (e) , p. 8, and 6.35, p. 104) 

(55) Calcium 

(55a) Calcium by Flame Photometer 

Apparatus 

Perkin-Elmer model 52 flame photometer with 
acetylene or propane burner. 



130 



AGRICULTURE HANDBOOK 60, U. S. DEPT. OF AGRICULTURE 



Reagents 

A. Lithium chloride, 0.05 N. Dissolve 2.12 gm. of 
lithium chloride in water and make to 1 liter. 

B. Sodium chloride, 5.00 meq./l. Dissolve 0.2922 
gm. of dry sodium chloride in water and make to 1 liter. 

C. Potassium chloride, 12.5 meq./l. Dissolve 0.9320 
gm. of dry potassium chloride in water and make to 1 
liter. 

D. Calcium chloride, 50.0 meq./l. Dissolve 2.503 
gm. of pure calcium carbonate (calcite crystals) in 
50 ml. of 3 N hydrochloric acid and dilute to 1 liter. 

E. Magnesium chloride, 50.0 meq./l. Dissolve 5.1 
gm. of MgCl 2 *6H 2 in approximately 900 ml. of water. 
Standardize by Method 78 and add the calculated 
amount of water to bring the magnesium concentra- 
tion to 50.0 meq./l. 

Remarks 

The optimum concentration of lithium chloride for 
use as an internal standard varies with individual flame 
photometers but is usually 5 to 10 meq./l. 

Interference by sodium, potassium, and magnesium 
is not an appreciable factor unless the concentration of 
the interfering element is at least 5 times the concentra- 
tion of calcium. Interference may be compensated for 
by determining the concentration of the interfering 
element (s) in the unknown and by adding this con- 
centration ( ±20 percent) of the interfering element (s) 
to the standard solutions. In the determination of 
calcium in plant tissue, interference is seldom en- 
countered. 

Procedure 

Prepare a series of standards containing 0, 1, 2, 3, 
and 4 meq./l. of calcium (0, 1, 2, 3, and 4 ml. of re- 
agent D per 50 ml.) and the concentration of lithium 
chloride found to be optimum for the instrument. 

Transfer an aliquot (usually 10 ml.) of the acid 
digest (Method 54a) containing 0.05 to 0.20 meq. of 
calcium to a 50-ml. volumetric flask and add the same 
concentration of lithium chloride used in the standard 
series. Add compensating solutions B, C, and E when 
necessary, and make to volume. Obtain instrument 
readings for standard solutions and unknowns with 
the wave-length indicator set at the point correspond- 
ing to the calcium emission maximum at 6,220 A. 

Calculations 

Milliequivalents of Ca per 100 gm. of dry material — 
(meq./l. of Ca from calibration curve ) X 500/ml. in 
aliquot. 

(556) Calcium by Oxalate Method 

The acid digest (Method 54a) may be analyzed for 
calcium by Method 77, if a flame photometer is not 
available. 



Calculations 

Milliequivalents of Ca per 100 gm. of dry material = 
normality of KMn0 4 X 10,000 X ( ml . of KMn0 4 - ml. of 
blank) /ml. in aliquot of acid digest. 

(56) Magnesium 

Remarks 

Methods for determining magnesium by the use of 
thiazole yellow or related dyes have not given acceptable 
results at this laboratory. The following method, while 
time-consuming, has proved to be reliable. The cal- 
cium is removed as the oxalate, and magnesium is pre- 
cipitated as magnesium ammonium phosphate hexahy- 
drate. The phosphate is determined colorimetrically, 
and magnesium is calculated by reference to a calibra- 
tion curve. 

Apparatus 

Photoelectric colorimeter or spectrophotometer. 
Reagents 

A. Oxalic acid, 1 N. Dissolve 63 gm. of oxalic acid 
in water and make to 1 liter. 

B. Methyl orange, 0.01 percent in 95 percent ethanol. 

C. Ammonium hydroxide, cone. 

D. Hydrochloric acid ( 1 + 1 ) . 

E. Magnesium chloride, 5.00 meq./l. Dissolve 0.51 
gm. MgCl 2 -6H 2 in approximately 900 ml. of water. 
Standardize by Method 78 and add the calculated 
amount of water to bring the magnesium concentration 
to 5.00 meq./l. 

F. Ammonium chloride, 3 percent. Filter before use. 

G. Ammonium dihydrogen phosphate, 5 percent. 
Filter before use. 

H. Phenolphthalein, 1 percent in 60 percent ethanol. 

I. Ammonium hydroxide in ethanol and ether. Mix 
20 ml. of concentrated ammonium hydroxide with 980 
ml. of a mixture of equal volumes of ethanol, ether, and 
water. 

J . Sulfuric acid ( 1 + 6 ) . 

K. Ammonium vanadate, 0.25 percent. Dissolve 2.5 
gm. of ammonium vanadate in 500 ml. of boiling water, 
cool somewhat, and then add 60 ml. of reagent J. Cool 
to room temperature and dilute to 1 liter. Store in a 
brown bottle. 

L. Ammonium molybdate, 5 percent. Store in a 
brown bottle. 

Procedure 

Transfer an aliquot (usually 10 ml.) of the acid 
digest from Method 54a containing 0.01 to 0.05 meq. 
of magnesium to a 25-ml. volumetric flask. Prepare a 
series of standards in 25-ml. volumetric flasks con- 
taining 0, 0.01, 0.02, 0.03, 0.04, and 0.05 meq. of 
magnesium (0, 2, 4, 6, 8, and 10 ml. of reagent E). 
To all standards and unknowns, add 3 drops of B, 



SALINE AND ALKALI SOILS 



131 



acidify with D, if necessary, and add 1 ml. of D in 
excess. Add 1 ml. of A, heat to boiling, and neutralize 
with C. Cool and add more C if necessary to keep 
basic (yellow). Make to volume and filter through a 
dry filter paper ; do not wash. Transfer a 5-ml. aliquot 
of the filtrate to a 15-ml. centrifuge tube and add 1 ml. 
each of F and G and 1 drop of H. Heat to about 90° C. 
in a water bath, and then add C until permanently pink. 
After 15 min., add an additional 2 ml. of C, stopper, 
mix, and let stand overnight. 

Centrifuge at RCF = 2,000 for 10 min., decant care- 
fully, drain on filter paper for 10 min., and wipe the 
mouth of the tube with a clean towel or lintless filter 
paper. Suspend the precipitate and rinse the sides of 
the tube with a stream of 5 ml. of reagent I from a pipet 
equipped with a rubber bulb. Centrifuge at RCF = 
2,000, decant, drain for 5 min., and wipe the mouth 
of the tube. Repeat this washing procedure once. 

Pipet 10 ml. of reagent J into the tube and twirl for 
a few seconds. After 5 min. transfer the contents 
quantitatively into a 100-ml. volumetric flask with a 
total of 50 ml. of water. Pipet 10 ml. each of K and L 
into the flask while swirling the solution rapidly. 
Make to volume and mix. After 10 min. measure the 
percent transmission of the unknown and standard 
solutions at 4,000 A. or by means of an appropriate 
blue filter. 

Calculations 

Milliequivalents of Mg per 100 gm. of dry material = 
(meq. of Mg from calibration curve) X 10,000/ml. in 
aliquot of acid digest. 

(57) Sodium 

(57a) Sodium by Flame Photometer 
Apparatus 

Perkin-Elmer model 52 flame photometer with acety- 
lene or propane burner. 

Reagents 

A. Lithium chloride, 0.05 N. Dissolve 2.12 gm. of 
lithium chloride in water and make to 1 liter. 

B. Sodium chloride, 5.00 meq./l. Dissolve 0.2922 
gm. of dry sodium chloride in water and make to 1 liter. 

C. Potassium chloride, 12.5 meq./l. Dissolve 0.9320 
gm. of dry potassium chloride in water and make to 1 
liter. 

D. Calcium chloride, 50.0 meq./l. Dissolve 2.503 
gm. of pure calcium carbonate (calcite crystals) in 50 
ml. of 3 N hydrochloric acid and dilute to 1 liter. 

E. Magnesium chloride, 50.0 meq./l. Dissolve 5.1 
gm. of MgCl 2 *6H 2 in approximately 900 ml. of water. 
Standardize by Method 78 and add the calculated 
amount of water to bring the magnesium concentration 
to 50.0 meq./l. 



Remarks 

The optimum concentration of lithium chloride for 
use as an internal standard varies with individual 
flame photometers, but is usually 5 to 10 meq./l. 

Sodium is frequently found in relatively small 
amounts in plant material, so that interference often 
occurs. Potassium interferes if the potassium : sodium 
ratio is 5 or greater; and calcium, if the calcium: 
sodium ratio is 10 or greater. Since these ratios are 
frequently exceeded in plant materials, it is advisable 
to determine calcium and potassium first, so that the 
approximate concentrations of interfering elements 
may be added to the sodium standard solutions. Mag- 
nesium does not cause interference unless magnesium : 
sodium ratios are in excess of 100. Such magnesium : 
sodium ratios are very rarely encountered. 

Procedure 

Prepare a series of standards containing 0, 0.1, 0.2, 
0.3, and 0.4 meq./l. of sodium (0, 1, 2, 3, and 4 ml. 
of reagent B per 50 ml.) and the concentration of 
lithium chloride found to be optimum for the instru- 
ment. 

Transfer an aliquot (usually 10 ml.) of the acid 
digest (Method 54a) containing 0.005 to 0.020 meq. 
of sodium to a 50-ml. volumetric flask and add the 
same concentration of lithium chloride used in the 
standard series. Add compensating solutions C, D, 
and E when necessary and make to volume. Obtain 
instrument readings for standard solutions and un- 
knowns with the wave-length indicator set at the point 
corresponding to the sodium emission maximum at 
5,890 A. 

Calculations 

Milliequivalents of Na per 100 gm. of dry material = 
(meq./l. of Na from calibration curve) X500/ml. in 
aliquot. 

(576) Sodium by Uranyl Zinc Acetate 

Reagents 

A. Uranyl zinc acetate. Weigh 300 gm. of uranium 
acetate dihydrate, 900 gm. of zinc acetate dihydrate, 
and 10 mg. of sodium chloride into a large flask. Add 
82 ml. of glacial acetic acid and 2,618 ml. of water. 
Stir or shake until the salts are dissolved, leaving only 
a small amount of sodium uranyl zinc acetate precipi- 
tate. This may require several days. Filter before use. 

B. Ethanol, saturated with sodium uranyl zinc ace- 
tate. Filter before use. Sodium uranyl zinc acetate 
may be prepared as follows: Add 125 ml. of reagent A 
to 5 ml. of 2 percent sodium chloride solution, stir, and 
after 15 min. collect the precipitate in a porous-bot- 
tomed porcelain crucible. Wash several times with 
glacial acetic acid, then several times with ether. Dry 
in a desiccator. 



132 



AGRICULTURE HANDBOOK 60, U. S. DEPT. OF AGRICULTURE 



C. Ether, anhydrous. 

D. Phenolphthalein, 1 percent in 60 percent ethanol. 

E. Calcium chloride dihydrate, 10 percent in water. 

F. Ammonium hydroxide (1 + 1). 

G. Acetic acid, 2 percent. 
H. Acetic acid, glacial. 

Procedure 

Transfer an aliquot (usually 25 ml.) of the acid 
digest (Method 54a) sufficient to give 50 to 200 mg. of 
sodium uranyl zinc acetate to a 50-ml. sugar flask. 
Add 1 drop of reagent D and 5 ml. of E and make the 
solution basic (pink) with F to precipitate phosphate. 
Make to 55 ml. and filter through a dry paper; do not 
wash. Transfer a 50-ml. aliquot to a 100-ml. beaker, 
acidify with H, and evaporate to dryness on a steam 
bath. Cool, dissolve the residue in 2 ml. of G, and add 
75 ml. of filtered reagent A. Stir the solution and allow 
to stand for 1 hr. Filter through a porous-bottomed 
porcelain filtering crucible, taking care to transfer all 
the sodium uranyl zinc acetate precipitate onto the 
filter by means of a small wash bottle filled with A. 
Wash the beaker 5 times with 2-ml. portions of A and 
pass the washings through the filter. Allow the crucible 
to drain completely, because it is important to have 
the filter and the precipitate free of the reagent before 
washing with the alcohol. Wash the crucible 5 times 
with 2-ml. portions of B and, after removing all the 
alcohol by suction, wash once or twice with C. The 
suction is continued until the precipitate is dry. Allow 
the crucible to stand in a desiccator for 2 hr. and weigh. 

Return the crucible to a suction apparatus and wash 
with small portions of water until all the soluble ma- 
terial is dissolved and passes through the crucible. 
Wash with alcohol and ether as above. Dry and weigh. 
The difference between the first and last weight 
represents the weight of sodium precipitate. The 
precipitate is assumed to have the composition: 
(U0 2 ) 3 NaZn (CH 3 COO) 9 -6H 2 ; molecular weight, 
1538.079; percent sodium, 1.4952. 

Calculations 

Milliequivalents of Na per 100 gm. of dry material = 
(gm. of sodium uranyl zinc acetate precipitate) X 
7,152/ml. in aliquot. 

(58) Potassium 

(58a) Potassium by Flame Photometer 

Apparatus 

Perkin-Elmer model 52 flame photometer with 
acetylene or propane burner. 

Reagents 

A. Lithium chloride, 0.05 N. Dissolve 2.12 gm. of 
lithium chloride in water and make to 1 liter. 



B. Sodium chloride, 5.00 meq./l. Dissolve 0.2922 
gm. of dry sodium chloride in water and make to 1 liter. 

C. Potassium chloride, 12.5 meq./l. Dissolve 0.9320 
gm. of dry potassium chloride in water and make to 1 
liter. 

D. Calcium chloride, 50.0 meq./l. Dissolve 2.503 
gm. of pure calcium carbonate (calcite crystals) in 50 
ml. of 3 N hydrochloric acid and dilute to 1 liter. 

E. Magnesium chloride, 50.0 meq./l. Dissolve 5.1 
gm. of MgCl 2 *6H 2 in approximately 900 ml. of water. 
Standardize by Method 78 and add the calculated 
amount of water to bring the magnesium concentration 
to 50.0 meq./l. 

Remarks 

The optimum concentration of lithium chloride for 
use as an internal standard varies with individual flame 
photometers but is usually 5 to 10 meq./l. 

Interference by sodium occurs if the sodium : potas- 
sium ratio is 5 or greater, and by calcium if the cal- 
cium : potassium ratio is 10 or greater. Magnesium 
does not cause interference until the magnesium : po- 
tassium ratio is in excess of 100. Interference in the 
determination of potassium is very rarely encountered. 

Procedure 

Prepare a series of standards containing 0, 0.25, 
0.50, 0.75, and 1.00 meq./l. of potassium (0, 1, 2, 3, 
and 4 ml. of reagent C per 50 ml.) and the concentra- 
tion of lithium chloride found to be optimum for the 
instrument. 

Transfer an aliquot (usually 10 ml.) of the acid 
digest (Method 54a) containing 0.01 to 0.05 meq. of 
potassium to a 50-ml. volumetric flask and add the 
same concentration of lithium chloride used in the 
standard series. Add compensating solutions B, D, 
and E when necessary and make to volume. Obtain 
instrument readings for standard solutions and un- 
knowns with the wavelength indicator set at the point 
corresponding to the potassium emission maximum at 
7,680 A. 

Calculations 

Milliequivalents of K per 100 gm. of dry material = 
(meq./l. of K from calibration curve) X500/ml. in 
aliquot. 

(58b) Potassium by Cobaltinitrite 

Reagents 

A. Nitric acid (1 + 15). 

B. Trisodium cobaltinitrite, 20 percent. Store at 
about 5° C. and filter before use. The solution is 
stable for some time but should be prepared fresh at 
about biweekly intervals. 

C. Nitric acid (1+1,500) . Dilute 10 ml. of reagent 
A to 1 liter. 



SALINE AND ALKALI SOILS 



133 



D. Ethanol, 95 percent. 

E. Potassium chloride, 0.0100 N. Dissolve 0.7456 
gm. of dry potassium chloride in water and make to 1 
liter. 

Procedure 

Evaporate to dryness in a 50-ml. beaker an aliquot 
(usually 25 ml.) of the acid digest (Method 54a) con- 
taining 0.05 to 0.35 meq. of potassium. Add 10 ml. 
of water, 1 ml. of reagent A, and stir to dissolve. Add 
5 ml. of B, stir and allow to stand for 2 hr. at 15° to 
20° C. Filter in a porous-bottomed porcelain filtering 
crucible, the tare weight of which is known, using C 
in a wash bottle to make the transfer. Wash 10 times 
with C and 5 times with 2-ml. portions of D. Aspirate 
until quite dry. Wipe the outside with a cloth, dry for 
1 hr. at 110° C, cool in a desiccator, and weigh. 

Prepare a series of standards containing 0, 0.05, 
0.15, 0.25, and 0.35 meq. of potassium (0, 5, 15, 25, 
and 35 ml. of reagent E) in 50-ml. beakers and proceed 
as directed for the aliquots of the acid digests. 

Calculations 

Milliequivalents of K per 100 gm. of dry material = 
(meq. of K from calibration curve) X 10,000/ml. in 
aliquot. 

(59) Chloride 

Remarks 

A modification of the method described by Clark 
and others (1942) has been found to give results in 
close agreement with those obtained by AOAC pro- 
cedures with a considerable saving in time. The sam- 
ple for chloride analysis together with a tube contain- 
ing acid and a well containing base are placed in a 
tightly closed weighing bottle (fig. 32). The acid 
digests the filter-paper plug in the acid tube and reacts 
with the sample, volatilizing chloride as hydrogen chlo- 
ride, which is absorbed by the potassium hydroxide. 
The absorbed chloride is then titrated with mercuric 
nitrate. 

Apparatus 

Make the following items from ordinary glass 
tubing: 

1. Acid tube, approximately 1.0 cm. inside diameter, 
with one end drawn out to a capillary tip. Capacity, 
2 ml. 

2. Outer well, approximately 1.1 cm. inside diameter, 
4 to 5 cm. long, sealed at one end. 

3. Inner well, approximately 1.0 cm. outside diame- 
ter, 1 to 2 cm. long, sealed at one end. 

4. Support for inner well of such length that when 
assembled, the top of inner well is at, or slightly above, 
the top of the outer well. 

Clamp. Any screw-type clamp, equipped with rub- 



GROUND GLASS 
J JOINT *■ 



OUTER WELL 



INNER WELL 
WITH KOH 



SUPPORT FOR 
INNER WELL — 



SAMPLE 



t ^:agfeg^^»^^?fi^ftOtVi-S^g 




30 ML. WEIGHING 
BOTTLE WITH 
OUTSIOE CAP 



ACID TUBE WITH 
H2SO4 



FILTER PAPER 
PLUG 



Figure 32. — Apparatus for the chloride determination 

(Method 59). 

ber cushions which will hold the cap securely on the 
weighing bottle. 

Caution. — After cleaning, rinse all glassware shown 
in figure 32 with nitric acid (1 + 100) and dry in oven. 
Use forceps, thereafter, in handling acid tubes, wells, 
and supports to avoid chloride contamination. Avoid 
contaminating the air with hydrogen chloride. 

Reagents 

A. Potassium hydroxide, 50 percent. 

B. Sulfuric acid, cone. 

C. Ethanol, 95 percent. 

D. Diphenylcarbazone, 1 percent. Dissolve 1 gm. 
of diphenylcarbazone (Eastman No. 4459) in 100 ml. 
of 95 percent ethanol. Store at 5° C. 

E. Mercuric nitrate, 0.01 N. Dissolve 1.7 gm. of 
Hg(N0 3 ) 2 -H 2 in water to which 10 ml. of nitric 
acid (1 + 7) have been added and make to 1 liter. 
Store in brown bottle in the dark. 

F. Potassium chloride, 50.0 meq./l. Dissolve 3.728 
gm. of dry potassium chloride in water and make to 1 
liter. 

G. Hydrogen peroxide, 30 percent. 
H. Nitric acid (1 + 7). 

I. Bromphenol blue, 0.05 percent in ethanol. 

Procedure 

Weigh accurately in a 30-ml. weighing bottle a 
sample (usually 0.1 gm.) of dried plant material con- 
taining 0.02 to 0.25 meq. of chloride. To determine 
chloride in expressed sap, evaporate a suitable aliquot 
(usually 1 ml.) to dryness in the weighing bottle at 
70° C. Prepare a series of standards containing 0, 
0.05, 0.10, 0.15, 0.20, and 0.25 meq. of chloride (0, 1, 
2, 3, 4, and 5 ml. of reagent F) and evaporate to dry- 
ness in the weighing bottles. 



134 



AGRICULTURE HANDBOOK 60, U. S. DEPT. OF AGRICULTURE 



Plug the acid tube with macerated filter paper and 
assemble the apparatus as shown in figure 32. Add 3 
drops of reagent A and 1 drop of C to the inner well. 
Add 2 ml. of B to the acid tube and moisten the ground 
surface of the cap with B. Seal the weighing bottle by 
twisting the cap into position and clamp securely. 
Place the assembly in an oven at 110° C. overnight. 
Remove, cool, and open the weighing bottles, using 
rubber gloves. 

Transfer the inner well with forceps to a porcelain 
casserole and add 5 ml. of water. Add 3 drops of 
reagent I, neutralize with H, dissolving all of the residue 
in the inner well, and add 1 drop of H in excess. Add 
3 drops of G, 1 drop of D, and titrate with E to a 
purple or pink color, depending on volume. Prepare 
a standard curve; it is not linear over the entire range. 

Calculations 

Milliequivalents of CI per 100 gm. dry material = 
(meq. of CI in sample) X 100/gm. of sample. 

Milliequivalents of CI per liter of sap= (meq. of CI 
in aliquot) X 1,000/ml. in aliquot. 

References 

Association of Official Agricultural Chemists (1950, 
6.41-6.46, p. 105, 106), Clark and others (1942). 

(60) Sulfur 

Reagents 

A. Hydrochloric acid, cone. 

B. Barium chloride, 10 percent. Filter before use. 

C. Methyl orange, 0.05 percent in ethanol. 

Procedure 

Transfer an aliquot (usually 50 ml.) of the digest 
(Method 54b) containing 0.1 to 2.0 meq. of sulfate to a 
250-ml. beaker. Add 2 drops of reagent C, acidify 
with A if necessary, and then add 1 ml. of A. Make to 
approximately 100 ml. with water, heat to boiling, and 
add an excess of B, drop by drop, with constant stirring. 
Cover with a watchglass and allow to stand on a steam 
bath for several hours, until the volume is reduced to 
approximately 50 ml. After cooling, filter the precipi- 
tate of barium sulfate through an ignited and weighed 
Gooch crucible and wash with water until free of 
chloride. Dry, ignite in a muffle at low red heat, cool, 
and weigh. Ashless filter paper may be used in place 
of the Gooch crucible, but the muffle in which the 
ignition is made must be well ventilated. 

Calculations 

Milliequivalents of total S (expressed as sulfate) per 
100 gm. of dry material = gm. BaS0 4 X 42,841/ml. in 
aliquot. 



(61) Phosphorus 

Phosphorus is retained quantitatively by both the 
magnesium nitrate ignition and wet digestion, provided 
the perchloric acid digest is not allowed to go to 
dryness. 

Apparatus 

A photoelectric colorimeter or spectrophotometer. 

Reagents 

A. Sulfuric acid (14-6). 

B. Ammonium vanadate, 0.25 percent. Dissolve 
2.5 gm. of ammonium vanadate in 500 ml. of boiling 
water, cool somewhat, and add 60 ml. of reagent A. 
Cool to room temperature and dilute to 1 liter. Store 
in a brown bottle. 

C. Ammonium molybdate, 5 percent. 

D. Potassium dihydrogen phosphate, 2.50 milli- 
moles/1. Dissolve 0.3404 gm. of potassium dihydro- 
gen phosphate in water and make to 1 liter. 

Procedure 

Transfer an aliquot (usually 5 ml.) of the solution 
prepared by Method 54a or 54b containing 0.002 to 
0.020 millimoles of phosphate to a 50-ml. volumetric 
flask. Prepare a series of standards containing 0, 0.005, 
0.010, 0.015, and 0.020 millimoles of phosphate (0, 2, 
4, 6, and 8 ml. of reagent D) . Add to each flask con- 
taining unknown or standard, 5 ml. each of A, B, and 
C successively, shaking the flask during each addition. 
Make to volume, allow to stand 15 to 30 min., and 
determine transmittance at 4,000 A., or by means of a 
suitable blue filter. 

Calculations 

Millimoles of phosphate per 100 gm. of dry ma- 
terial = (millimoles of phosphate from calibration 
curve) X 10,000/ (ml. in aliquot Xgm. of sample di- 
gested) . 

1 millimole of phosphate =1 meq. of H 2 P0 4 ". 

(62) Boron 

Remarks 

Leaf samples, collected and prepared according to 
Method 53, are usually the best index to the boron status 
of the plant. 

Apparatus 

A spectrophotometer or photoelectric colorimeter. 

Alkali-resistant (boron-free) glassware, porcelain- 
ware, platinum, or fused-quartz dishes. Avoid the use 
of borosilicate glassware. 



SALINE AND ALKALI SOILS 



135 



Reagents 

A. Calcium oxide, powdered. 

B. Hydrochloric acid (1 + 1). 

C. Hydrochloric acid, cone. 

D. Sulfuric acid, cone. 

E. Carmine, 0.05 percent by weight in cone, sulfuric 
acid (0.920 gm./l.). Shake until completely dissolved. 

F. Boric acid, 100 p. p. m. boron. Dissolve 0.5716 
gm. of boric acid in water and make to 1 liter. 

Procedure 

Weigh a portion of the dry sample (usually 2.000 
gm.) containing not more than 1.00 mg. of boron and 
transfer to a porcelain casserole or platinum dish. Add 
0.1 gm. of reagent A per gram of sample and mix well. 
Ignite as completely as possible in a muffle at 500° to 
550° C, cool, and moisten with water. Cover with a 
watchglass and introduce 3 ml. of B per gram of sam- 
ple, which should make the solution strongly acid. 
Heat on a steam bath for 20 min. Transfer quanti- 



tatively to a 100-ml. volumetric flask, make to volume 
with water, and filter through a dry filter paper. 

Prepare a series of standard solutions containing 
to 10 p. p. m. boron (0 to 1.00 mg./lOO ml.) by 
diluting 0, 2, 4, 6, 8, and 10 ml. of reagent F to 100 ml. 
Pipet 2 ml. of each of the standards and of the un- 
knowns into Erlenmeyer flasks. Add 2 drops of C to 
each standard and 2 drops of water to each unknown. 
Add 10 ml. of D to each Erlenmeyer flask, mix, and 
cool. Add 10 ml. of E, mix, and allow to stand at least 
45 min. for color development. Determine the trans- 
mittance at 5,850 A., or by means of a suitable yellow 
filter. 

Calculations 

Parts per million B in dry plant material— (p. p. m. B 
from calibration curve) X 100/ gm. of sample. 

Reference 

Hatcher and Wilcox (1950). 



Chapter 8 



Methods of Analysis of Irrigation Waters 



[See the introductory notes at the beginning of chapter 6.] 



(70) Collection of Irrigation Water 
Samples 

The minimum quantity of water required for the 
ordinary chemical analysis is about one-half gallon 
(1.9 liters) . In special cases, larger quantities may be 
necessary. 

Care should be taken to obtain a representative 
sample. Satisfactory samples of some waters can be 
obtained only by mixing several portions collected at 
different times, the details as to collection and mixing 
depending on local conditions. Samples from wells 
should be collected after the pump has been running 
for some time, and samples from streams should be 
taken from running water. 

In general the shorter the elapsed time between col- 
lection and analysis of a sample, the more reliable will 
be the analytical data. Changes resulting from chemi- 
cal and biological activity may alter the composition 
of the sample. No satisfactory method for sterilizing 
a water sample to prevent bacterial action has been 
proposed. 

References 

American Public Health Association and American 
Water Works Association (1946, p. 1) . 

( 71 ) Records, Reports, and Expression of 
Results 

At the time of collection, a label, bearing a short 
identifying description, should be attached to the bottle. 
Additional information can be recorded on a "Col- 
lector's Description of Water Sample" form as shown. 
One item not specifically called for on this form, but 
often of importance, is the elevation above sea level of 
an appropriate reference point at the well. When this 
is known, it is possible to refer the water level in the 
well to sea level. This value may be useful in quality- 
of-water studies. The importance of an accurate and 
complete description, especially as regards location, 
cannot be overemphasized. 

Two other blank forms used at the Laboratory in 
connection with the analyses of water samples are 
shown on pages 138 and 139. The laboratory work 

136 



sheet is used for recording the original data obtained 
from the chemical analysis. One such sheet is used for 
each sample. A laboratory number is assigned which, 
with the description from the "Collector's Description of 
Water Sample," is entered at the top of the page. Upon 
completing and recording each separate determination, 
the analyst enters his initials and the date. 

For purposes of uniformity, the following rules for 
reporting analytical results are used : 

pH. — Report to the nearest 0.1 unit. 

Electrical conductivity (ECXIO 6 at 25° C.).— 
Report to the nearest 0.1 when less than 100, and to 3 
significant figures for values above 100. 

Dissolved solids. — Report in parts per million 
(p. p. m.) to the nearest whole number, but not more 
than 3 significant figures. 

Boron. — Electrometric titration method; report to 
the nearest 0.01 p. p. m. when less than 10 p. p. m. 
boron, and to 3 significant figures above 10 p. p. m. 
boron. 

Colorimetric method; report to the nearest 0.1 
p. p. m. boron but not more than 2 significant figures. 

Silica. — Report in p. p. m. Si0 2 to nearest whole 
number, but not more than 3 significant figures. 

Fluoride. — Report to the nearest 0.1 p. p. m. 
fluoride or to the nearest 0.01 meq./l. 

Cations and anions. — Report to the nearest 0.01 
meq./l. up to 100, and to 4 significant figures if above 
100 meq./l. 

( 72 ) Electrical Conductivity 
Remarks 

Electrical conductivity is commonly used for indi- 
cating the total concentration of the ionized constituents 
of a natural water. It is closely related to the sum of 
the cations (or anions) as determined chemically, and 
it usually correlates closely with the total dissolved 
solids. It is a rapid and reasonably precise determina- 
tion that does not alter or consume any of the sample. 

Apparatus 

Wheatstone bridge, alternating current, suitable for 
conductivity measurements. This may be a 1,000-cycle 
a. c. bridge with telephone receivers, a 60-cycle a. c. 



SALINE AND ALKALI SOILS 



137 



Collector's No. 



Name and/or owner 



United States Department of Agriculture 

Agricultural Research Service 

Soil and Water Conservation Research Branch 

United States Salinity Laboratory 

Riverside, California 

COLLECTOR'S DESCRIPTION OF WATER SAMPLE 



.; Lab. No. 



.; Date 



Collector 



Spring, Stream, Lake, Well? (circle one) 



Countv 



Location 



K 



, Sec. 



Miles — distance nearest town 
; T ; R 



Other description 

Depth ; Depth to upper perforation 



.; Casing diameter 



Discharge 
Temp. 



.; Static level 



.; Draws down to 



° C. or °F. 



.; Odor 



.; Gas 



.; Color 



Use: Irrig., Municipal, Ind., Stock, Domestic 
Approximate acreage served, crops 



Condition or symptoms of land or crops 

Owner's opinion of water quality 

Collector's remarks 



USGS sheet 



Distance and direction from section corner 

or landmark 



Report to: 



(Please draw a map on the reverse side, if necessary, to show the exact location of the sampling site). 



259525 O - 54 - 10 



138 



AGRICULTURE HANDBOOK 60, U. S. DEPT. OF AGRICULTURE 



Water sample No ♦ . Description: 






Dissolved Solids 


Boron 


Sum of 
Cations 


pH 








Sum of 
Anions 


Conductivity at 25°C . 

T°C # 
k . 


ECxlQS 
Anions 


Percent 

Na 


R 












ECxlO 6 
@ 25° C. 




D,S« 
p«p«nu 




B 
p«p#m# 












Calc 


ium 


Magpies 


ium 


Sodium 


Potassium 


Ca 
meq./U 




Mg 
meq*/! • 




Na 
meq«/U 




K 
meq./l # 












_. 








Carbonai 
Bicarb* 


be and 
:>nate 


Sulfate 


Chloride 


Nitrate 


co 3 

meq»/l» 

HC0 3 
meq#/l* 


















so 4 

meq # /l« 




CI 
meq«/l# 




N0 3 
meq»/l# 


























Received laboratory: 


Analysis completed: 


Reported : 














Reported to: 


















I 













SALINE AND ALKALI SOILS 



139 



UNITED STATES DEPARTMENT OP AGRICULTURE 
Agricultural Research Service 



Division of Soil and 
Plant Relationships 



U. S # Salinity Laboratory 
Rubidoux Unit 
Riverside, California 



REPORT OF WATER ANALYSIS 



Description 



Conductivity, ECxl0G©25°C. 



Percent Sodium 



Boron (B) parts per million 



u. 



Dissolved Solids: 

tons per acre -foot 
parts per million 

Hydrogen-ion activity (pH) 
Silica (SiC^) parts per million 



Cations 



Calcium 



(Ca) 



Magnesium (Mg) 



Sodium 



(Na) 



Potassium (K) 



Sum 



Milligram 
equivalents 

per liter 



Jferts per 
million 



XXX 



Anions 



Carbonate 

Bicarbonate 

Sulfate 

Chloride 
Fluoride 
Nitrate 



(C0 3 ) 
(HCOj) 

(so 4 ) 

(CI) 

(F) 

(N0 3 ) 



Sinn 



Milligram 
equivalents 

per liter 



ffcrts per 

million 



XXX 



Analysed by: 



Reported by: 



Reported to: 



140 



AGRICULTURE HANDBOOK 60, U. S. DEPT. OF AGRICULTURE 



bridge with an a. c. galvanometer, or one of the newer 
bridges employing a cathode ray tube as the null 
indicator. 

Conductivity cell, either pipet or immersion type, 
with platinized platinum electrodes. The cell constant 
should be approximately 1.0 reciprocal centimeter. 
New cells should be cleaned with chromic-sulfuric acid 
cleaning solution, and the electrodes should be 
platinized before use. Subsequently, they should be 
cleaned and replatinized whenever the readings become 
erratic or when an inspection shows that any of the 
platinum black has flaked off. The platinizing solution 
contains platinum chloride, 1 gm.; lead acetate, 0.012 
gm.; in 100 ml. water. To platinize, immerse the elec- 
trodes in the above solution and pass a current from a 
1.5-volt dry battery through the cell. The current 
should be such that only a small quantity of gas is 
evolved, and the direction of current flow should be 
reversed occasionally. 

Reagents 

A. Standard potassium chloride solution, 0.01 N. 
Dissolve 0.7456 gm. of potassium chloride in distilled 
water and make to 1 liter at 25° C. This is the stand- 
ard reference solution and at 25° C. has an electrical 
conductivity of 1411.8X10-° (0.0014118) mhos/cm. 

Procedure 

Place 4 tubes of reagent A in a water bath. ( For 
subsequent sets of determinations, discard the first tube 
of potassium chloride solution, shift the others one 
place, and insert a tube of fresh solution.) Place 2 
tubes of each sample in the bath, adjust the temperature 
to approximately 25° C, and hold at this temperature 
for 20 to 30 min. If the room temperature is not close 
to 25° C, it is better to adjust the temperature of the 
bath to approximately that of the room and hold it at 
that temperature until equilibrium is attained. The 
bath temperature is here represented by t. Rinse the 
electrode in three of the tubes of potassium chloride 
solution, transfer to the fourth, and measure the cell 
resistance (R' t ). Rinse the electrode several times in 
one tube of the water sample, transfer to the other 
tube, and read the resistance (R t )* The electrical con- 
ductivity (EC at 25° C.) of the sample is calculated 
from the equation : 

0.0014118 Xfi't 



using as an example a western surface water with a 
conductivity of 0.00117 mho/cm.: 



EC= 



Rt 



This is multiplied by 1,000,000 (10 6 ) and reported as 
ECX 10 6 at 25° C, or as EC, micromhos/cm. at 25°. 

The expression "electrical conductivity" is synony- 
mous with "specific electrical conductance." The stand- 
ard unit for conductivity is the mho/cm. It is so large 
that most natural waters have a value of much less 
than 1 unit. For purposes of convenience in recording 
or expressing such results, the value in mhos/cm. is 
multiplied by 10 G (decimal point moved 6 places to the 
right) and reported as EC X 10 6 at 25° C. The several 
methods of reporting conductivity are shown below, 



EC 

£CX10 3 
ECXIQr* 
ECX 10* 



0.00117 mho/cm. 
1.17 mmhos/cm. 
117 (-KX10 5 ) 
1,170 micromhos/cm. 



References 

Wilcox (1950), National Research Council, Inter- 
national Critical Tables (1929, v. 6, p. 234) . 

(73) Boron 

(73a) Boron, Electrometric Titration 

Remarks 

The addition of mannitol to a neutral, unbuffered 
solution of mixed salts containing boron causes the 
solution to become acid. The quantity of standard 
alkali required to titrate the solution back to the initial 
pH is an accurate measure of the boron present. Elec- 
trometric or direct methods of titration may be used. 

The choice of apparatus for the electrometric titra- 
tion of boron should be determined by the instruments 
available, the number of analyses to be made, and the 
frequency of use. Three sets of apparatus are de- 
scribed below, any one of which will give satisfactory 
results. The first requires a minimum of equipment. 
The operation depends on the fact that a 0.7 N calomel 
electrode and a quinhydrone electrode come to a null 
point (reversal of polarity) at approximately pH 7.0. 

Apparatus 

Galvanometer. An enclosed lamp and scale type 
sensitive to 0.025 microampere per scale division. 

Quinhydrone electrode. A piece of platinum wire 
7.5 cm. (3 in.) in length, with suitable contact above 
the surface of the solution. This type is preferable to 
an electrode of platinum sealed through glass and con- 
nected with mercury, as minute cracks develop in the 
glass and cause erratic results. 

Calomel electrode, 0.7 N with respect to potassium 
chloride. A silver-silver chloride electrode can be used 
in place of the 0.7 N calomel electrode. For details see 
Wilcox (1932). 

Motor -driven stirrer. 

Switch, single-pole single-throw. 

The electrodes are connected through the switch to 
the galvanometer. A shunt to protect the galvanometer 
is desirable but not essential. 

The second apparatus is a simple potentiometer 
(fig. 33). In addition to the parts listed above, the 
following are required: resistance wire, 1,500 ohms 
tapped at 60 ohms; and a 1.5-volt dry cell. A calomel 
electrode, 0.1 N with respect to potassium chloride, is 
substituted for the 0.7 N electrode described above. 

The third apparatus makes use of either a poten- 
tiometer or a pH meter as the indicating system. The 



SALINE AND ALKALI SOILS 



141 



110 VOLTS - AC 

T 



GALVANOMETER 



TRAN SF ORMER 
oN>— cJIE> ■ 



S.RS.T. 
SWITCH 



D.RS.T. A A 
SWITCH 66 



uj 



DRY CELL 1.5 VOLTS 



FIXED RESISTANCE 



o 
a 



IBEAKE 



6(> I 1440 OHMS 
OHMS 1 




J5 CALOMEL 



w 



— oNo— 
S.P.S.T 
SWITCH 



opIxt. 

SWITCH 



Figure 33. — Diagram of electrometric titration apparatus, 
showing electrical circuit. The 6 volt a. c. line from the 
transformer supplies the light in the reflecting galvanometer. 



instrument is set so that, at balance, the solution under 
test will have a pH reading of 7.1. The following 
electrode pairs have been found satisfactory: quinhy- 
drone and 0.1 N calomel; quinhydrone and saturated 
calomel; glass and saturated calomel. 

Reagents 

A. Quinhydrone, reagent quality, free from heavy 
metals. 

B. Bromthymol blue indicator solution, 1 percent. 
Methyl red may be substituted. 

C. Sulfuric acid. Approximately 1 N. 

D. Sulfuric acid. Approximately 0.02 N. 

E. Sodium hydroxide. Approximately 0.5 N, 
carbonate-free. 

F. Sodium hydroxide. Standard 0.0231 N, carbo- 
nate-free (1 ml. is equivalent to 0.25 mg. boron). 

G. Boric acid solution. Dissolve 0.5716 gm. dry 
H3BO3 in distilled water and dilute to 1 liter. The 
H3BO3 may be dried in a desiccator with calcium 
chloride. One ml. contains 0.1 mg. boron. This solu- 
tion is used in standardizing reagent F. 

H. Mannitol, neutral. Synthetic mannitol is prefer- 
able to the natural product. The "blank" titration for 
5 gm. of mannitol should not exceed 0.1 ml. of 
reagent F. 



Procedure 

Transfer an aliquot of the sample, containing not 
more than 1 mg. boron, to a 400-ml. beaker and dilute, 
if necessary, to 250 ml. Add a few drops of reagent B 
and acidify with C, adding 0.5 to 1 ml. in excess. Bring 
to boil, stir, cautiously at first, then vigorously, to expel 
carbon dioxide. Cool to room temperature, preferably 
in a water bath. With the S. P. S. T. switch open and 
the shunt, if used, set at 0.1, introduce the electrodes 
and stirrer into the solution. Start the stirrer and 
add E to approximate neutrality as shown by B. Add 
about 0.2 gm. of A and close the switch in the electrode 
circuit. The galvanometer should indicate approxi- 
mate balance. If it swings to the right, excess alkali 
is indicated, and if to the left, excess acid. Adjust 
with either F or D until the galvanometer shows no 
deflection. 

If a shunt is used, reverse the switch, thus eliminat- 
ing it from the circuit and permitting the galvanometer 
to function at its greatest sensitivity. Again adjust to 
balance with either dilute acid or alkali. The galva- 
nometer should be steady, showing at most only a slow 
drift. This is the initial point of the titration. Bring 
the shunt into the circuit by reversing the D. P. D. T. 
switch or open the S. P. S. T. switch, if the shunt is 
omitted. Add 5 ±0.1 gm. of mannitol. If boron is 
present, the indicator will change to the acid color and 
the galvanometer will swing to the left. Add reagent F 
until approximate balance is again attained; eliminate 
the shunt, if used, and complete the titration, bringing 
the galvanometer back to the original null point. This 
is the end point. 

Note the number of milliliters of reagent F required 
after adding the mannitol at the initial point of the 
titration. From this, subtract a blank determined by 
substituting distilled water for the sample and proceed 
as indicated above. The net volume of F multiplied 
by the equivalency (mg. boron per ml. NaOH) gives 
milligrams of boron in the aliquot titrated. Report as 
parts per million boron. The equivalency of F is 
established by titrating an aliquot of G. The buret 
used should be of such accuracy that the volume of F 
can be read to 0.01 ml. Borosilicate glassware (Pyrex) 
can be used for this determination. New beakers 
should be cleaned by filling with acid and heating on 
the steam bath before use. If the concentration of 
phosphate exceeds 10 p. p. m., it should be precipitated 
with lead nitrate and the excess lead removed with 
sodium bicarbonate. 

Calculations 

Parts per million B=(ml. NaOH-blank) Xmg. B 
equivalent to 1 ml. NaOH X 1,000/ml. in aliquot. 

References 

American Public Health Association and American 
Water Works Association (1946, p. 87-90), Associa- 
tion of Official Agricultural Chemists (1950, 31.52, 
p. 547), Wilcox (1932). 



142 



AGRICULTURE HANDBOOK 60, U. S. DEPT. OF AGRICULTURE 



( 73b ) Boron, Colorimetric, Using Carmine 

Apparatus 

A spectrophotometer with matched square cuvettes. 18 
Centrifuge tubes, flasks, beakers, pipets, and burets 
(boron-free glass). Alkali-resistant (boron-free) 
glassware, porcelainware, platinum, or fused quartz 
dishes are satisfactory. The use of borosilicate glass- 
ware is to be avoided. Convenient sizes are centrifuge 
tubes, 15-mL; flasks, 125-ml. ; beakers, 100-ml.; pipets, 
2-ml. ; burets, 10-ml. automatic. 

Reagents 

A. Sodium hydroxide, approximately 0.1 N, boron- 
free. 

B. Hydrochloric acid, cone. 

C. Hydrochloric acid, dilute (5 ml. cone. + 95 ml. 
water). 

D. Sulfuric acid, cone. 

E. Carmine solution. A 0.05 percent solution by 
weight of carmine in cone, sulfuric acid (0.920 gm./l.). 
Shake until completely dissolved. 

F. Standard boric acid solution. Stock solution. 
Dissolve 0.5716 gm. of recrystallized H 3 B0 3 in distilled 
water and dilute to 1 liter. One ml. of this solution 
contains 0.100 mg. of boron. 

Preparation of the Standard Curve 

Dilute portions of reagent F to obtain standards over 
the range of to 10 p. p. m. boron. Treat 2 ml. of each 
solution as described under Procedure and determine 
percent transmittance. For a reference, 2 ml. of dis- 
tilled water is carried through the entire procedure and 
set at 100 percent transmittance. 

Procedure 

Pipet 2 ml. of the sample which should contain not 
more than 0.02 mg. boron into an Erlenmeyer flask. 
Add 2 drops of reagent B. Add 10 ml. of D. Mix 
and cool. Add 10 ml. of E, mix, and allow to stand at 
least 45 min. for color development. Determine the 
percent transmittance at 585 m/x against a reference 
solution of 2 ml. of distilled water carried through the 
entire procedure. For colored samples such as certain 
soil extracts, follow the procedure under paragraph 
headed "Boron Concentration Too Low," except ignite 
gently after evaporating the sample to dryness. 

Calculations 

Read the boron concentration from the concentra- 
tion-transmittance calibration graph. Where the boron 
concentration is such that the measured transmittance 
value falls outside the recommended portion of the 
transmittance range (this method suggests 20 to 95 

18 A Coleman Model 14 Universal spectrophotometer with 13 
by 13 by 105 mm. matched square cuvettes and filter PC-4 is 
quite satisfactory. Any good photoelectric colorimeter should 
be adequate, although perhaps somewhat less accurate. 



percent), the sample is either diluted or concentrated 
to meet these conditions. 

Boron Concentration Too Great. — Dilute the 
sample with distilled water to a known volume, mix, 
pipet 2 ml. into an Erlenmeyer flask, and proceed as 
directed above. 

Boron Concentration Too Low. — Pipet a suitable 
aliquot of the sample into a beaker, a platinum dish, 
or other suitable vessel. Make alkaline with reagent A 
and add a slight excess. (The same amount should be 
added to all samples, including a reference.) Evapo- 
rate to dryness on a steam bath or in an oven at 95° C. 
Cool, add 5 ml. of C, and triturate with a rubber 
policeman. Pour the solution into a conical centrifuge 
tube and centrifuge at RCF= 1,000 to 1,500. Pipet 2 
ml. of the clear solution into an Erlenmeyer flask and 
follow the procedure shown above, correcting the read- 
ing from the standard curve to conform with the 
aliquot taken. 

Reference 

Hatcher and Wilcox ( 1950) . 

(74) Dissolved Solids 

Procedure 

Filter the sample to obtain a perfectly clear liquid. 
Evaporate a suitable aliquot containing not more than 
1.0 gm. of residue to dryness in a weighed platinum 
dish. Dry to constant weight at 105° C. Cool in a 
desiccator and weigh. Reserve for the determination 
of silica under Method 76. 

Calculations 

Parts per million DS~ gm. residue X 1,000,000/ml. 
in aliquot. 

Reference 

Association of Official Agricultural Chemists (1950, 
31,3, p. 535) . 

(75) pH of Waters 

Procedure 

See Method 21c. 

(76) Silica 

(76a) Silica, Gravimetric 

Procedure 

Acidify the sample or the residue from Method 74 
with hydrochloric acid and evaporate to dryness on a 
steam bath in a platinum dish. Continue the drying 
for about an hour. Thoroughly moisten the residue 



SALINE AND ALKALI SOILS 



143 



with 5 to 10 ml. hydrochloric acid. Allow to stand 
10 to 15 min. and add sufficient water to bring the 
soluble salts into solution. Heat on a steam bath until 
solution of salts is effected. Filter to remove most of 
the silica and wash thoroughly with hot water. Evapo- 
rate the filtrate to dryness and treat the residue with 
5 ml. hydrochloric acid and sufficient water to effect 
solution of soluble salts, as before. Heat, filter, and 
wash with hot water. Transfer the 2 residues to a 
platinum crucible, ignite in a muffle furnace, cool, and 
weigh. Moisten the contents of the crucible with a 
few drops of water. Add a few drops of sulfuric acid 
and a few milliliters of hydrofluoric acid and evapo- 
rate on a steam bath under a hood. Repeat the treat- 
ment if all the silica is not volatilized. Dry carefully 
on a hot plate, ignite, cool, and weigh. The difference 
between the two weights is the weight of silica. 

Calculations 

Parts per million Si0 2 = gm. Si0 2 X 1,000,000/ml in 
aliquot. 

Reference 

Association of Official Agricultural Chemists (1950, 
31.19, p. 539). 



( 76b ) Silica, Colorimetric 



19 



Apparatus 

Spectrophotometer or photoelectric colorimeter. 

Reagents 

A. Ammonium molybdate solution, 20 percent, stock 
solution. Dissolve 50 gm. (NH 4 ) 6 Mo 7 24 -4H 2 in 200 
ml. water (do not heat) , make to 250 ml. and filter. 

B. Sulfuric acid, 10 N. Add 70.2 ml. cone, sulfuric 
acid with stirring to 185 to 190 ml. water, cool, transfer 
to 250-ml. volumetric flask, and dilute to the mark. 
Solutions A and B may be stored in glass because of 
the small amount used per determination. 

C. Ammonium molybdate, sulfuric acid mixture. 
Add 1 ml. of reagent B and 2 ml. of A to 200 ml. of 
water. Use 10 ml. for each determination. A fresh 
lot of this reagent should be prepared for each set of 
samples. 

D. Standard silica solution, 50 p. p. m. Si0 2 . To 
prepare, dissolve more than the calculated amount of 
crystalline Na 2 Si0 3 -9H 2 in water, filter, and analyze 
gravimetrically, as described under Method 76a. Add 
the calculated amount of water necessary to dilute the 
solution to exactly 50 p. p. m. Si0 2 . Store in a poly- 
ethylene bottle, not in glass. 

19 This method was adapted for use with a spectrophotometer 
from a method proposed by Scripps Institution of Oceanography 
at La Jolla, California. 



Preparation of the Standard Curve 

Dilute portions of reagent D to obtain standards 
over the range of to 50 p. p. m. Si0 2 . Treat 1 ml. of 
each solution as described under "Procedure" and de- 
termine percent transmittance. 

Procedure 

To 1 ml. of the sample add 10 ml. of reagent C and 
mix thoroughly. Determine the percent transmittance 
after standing 10 min., but not more than 45 min., at 
350 m/x against a reference solution of 1 ml. of distilled 
water carried through the entire procedure. Read the 
silica concentration from the standard curve and report 
asp. p. m. Si0 2 . 

(77) Calcium 
Reagents 

A. Bromcresol green (sodium salt), 0.1 percent in 
water. 

B. Hydrochloric acid, 6 N. 

C. Oxalic acid solution, 1 N. Dissolve 63 gm. 
(COOH) 2 -2H 2 in 1 liter of water. 

D. Ammonium hydroxide solution (1 + 1). 

E. Sulfuric acid, dilute solution (45 ml. water plus 
5 ml. cone, sulfuric acid). 

F. Standard potassium permanganate, 0.05 N. 

Procedure 

Take an aliquot of the sample containing between 
0.20 and 2.0 meq. of calcium and concentrate, if neces- 
sary, to a volume of approximately 200 ml. Add 2 to 3 
drops of reagent A, acidify with B, and then add 0.5 ml. 
of B and 0.5 ml. of C for each 100 ml. of solution. 
Heat to boiling and neutralize with D. An excess of C 
is added gradually (5 ml. for each 100 ml. of solution) 
with constant stirring; the hot solution is made slightly 
alkaline with D and allowed to boil gently for several 
minutes. Cool and let stand until the precipitate of 
calcium oxalate settles. During the cooling, further 
additions of D may be necessary, in order to keep the 
solution faintly alkaline. 

Filter through a good grade filter paper designed 
for fine precipitates, receiving the filtrate in a 400-ml. 
beaker. Reserve the filtrate for the determination of 
magnesium. Transfer the precipitate to the filter paper 
and wash both beaker and precipitate with water until 
free from soluble oxalates. Remove the beaker con- 
taining the filtrate and substitute the original beaker. 
Puncture the tip of the filter paper and wash the pre- 
cipitate down into the beaker. Pour 50 ml. of reagent 
E through the funnel and rinse with water. The beaker 
is heated nearly to boiling and the liberated oxalic acid 
titrated with F until faintly pink. Add the filter paper 
and continue the titration until a very slight permanent 
pink color appears. 



144 



AGRICULTURE HANDBOOK 60, U. S. DEPT. OF AGRICULTURE 



Calculations 

Milliequivalents per liter of Ca= 1,000 X normality 
of KMn0 4 X (ml. KMn0 4 - blank) /ml. in aliquot. 

Reference 

Blasdale (1909). 

( 78 ) Magnesium 

Reagents 

A. Hydrochloric acid ( 1 + 1 ) . 

B. Diammonium-hydrogen phosphate solution. Make 
up a 20 percent solution of diammonium-hydrogen 
phosphate in water. Filter before use. A fresh lot of 
this reagent should be prepared for each set of samples. 

C. Ammonium hydroxide solution (1 + 1). 

D. Ammonium hydroxide, cone. 

Procedure 

Acidify the filtrate from the calcium determination 
(Method 77) with reagent A then add 2 ml. in excess. 
Evaporate on a hot plate. If the weight of pyrophos- 
phate is expected to be 0.0500 gm. or more, reduce the 
volume to 100 ml. ; otherwise, evaporate to 50 ml. and 
allow to cool. Add 5 ml. of B for each 50 ml. volume, 
then C drop by drop with stirring, until the solution is 
strongly alkaline. After a few minutes add 10 ml. of D 
for each 100 ml. final volume. On the following day, 
filter on ashless paper and wash with dilute ammonium 
hydroxide (5 + 95). Transfer the paper with the pre- 
cipitate to a weighed silica or porcelain crucible, dry, 
and ignite to whiteness in a muffle. Cool in a desiccator 
and weigh. 

Calculations 

Milliequivalents per liter of Mg=gm. Mg 2 P 2 7 X 
17,969/ml. in aliquot. 

Reference 

Association of Official Agricultural Chemists (1950, 
31 26, p. 541). 

(79) Calcium and Magnesium by the Ver- 

senate Method 

Procedure 

See Method 7. 

(80) Sodium 

(80a) Sodium by Uranyl Zinc Acetate, 
Gravimetric 

The method of Barber and Kolthoff is the basis for 
the one here described. It has been modified in only 
minor details. 



Reagents 

A. Uranyl zinc acetate: 

Uranyl acetate, dihydrate 300 gm. 

Zinc acetate, dihydrate 900 gm. 

Acetic acid, 30 percent 270 ml. 

Distilled water 2,430 ml. 

Weigh the salts and transfer to a large flask; add 
acetic acid and water; shake or stir occasionally until 
the salts are dissolved. This may take several days. 
Filter before use. 

B. Ethyl alcohol, saturated with sodium-ur anyl-zmc- 
acetate precipitate. Filter before use. 

C. Ether, anhydrous. 

Procedure 

Evaporate an aliquot of water sufficient to give 50 
to 200 mg. of the triple salt (usually 10 to 20 ml.) in a 
Pyrex beaker to a volume of 1 to 2 ml. Cool. Add 20 
ml. of the filtered reagent A. Stir the solution and allow 
to stand for 1 hr. Filter through a porous-bottomed 
porcelain filtering crucible, taking care to transfer all 
the triple salt onto the filter by means of a small wash 
bottle filled with A. Wash the beaker 5 times with 
2-ml. portions of A and pass the washings through the 
filter. Allow the crucible to drain completely, because 
it is important to have the filter and the precipitate 
free from the reagent before washing with the alcohol. 
Wash the crucible 5 times with 2-ml. portions of B and, 
after removing all the alcohol by suction, wash once 
or twice with C. The suction is continued until the 
precipitate is dry. Allow the crucible to stand in a 
desiccator 2 hr. and weigh. 

Return the crucible to a suction apparatus and wash 
with small portions of water until all the soluble ma- 
terial is dissolved and passes through the crucible. 
Wash with alcohol and ether as above. Dry and weigh. 
The difference between the first and last weight repre- 
sents the weight of sodium precipitate. The precipi- 
tate is assumed to have the composition (U0 2 ) 3 NaZn 
(CH 3 COO) 9 -6H 2 0; molecular weight, 1538.079; per- 
cent sodium, 1.4952. 

Calculations 

Milliequivalents per liter of Na^gm. sodium-uranyl- 
zinc-acetate precipitate X 650.16/ml. in aliquot. 

Reference 

Barber and Kolthoff ( 1928 ) . 

(80b) Sodium by Flame Photometer 

Procedure 

See Method 10a. 

(81) Potassium 



SALINE AND ALKALI SOILS 



145 



(81a) Potassium by Cobaltinitrite, Gravi- 
metric 

Reagents 

A. Nitric acid, 1 N. 

B. Trisodium cobaltinitrite solution. Prepare an 
aqueous solution containing 1 gm. of the salt of reagent 
quality in each 5 ml., allowing 5 ml. for each determina- 
tion. Filter before use. The solution is stable for 
some time, but it is preferable to make up a fresh lot 
before each set of determinations. 

C. Nitric acid, 0.01 N. 

D. Ethyl alcohol, 95 percent. 

Procedure 

The aliquot for analysis should contain between 2 
and 15 mg. of potassium in a neutral aqueous solution 
of 10-ml. volume. (Ammonia interferes and if present 
must be removed by evaporation with sodium hydrox- 
ide.) Add 1 ml. of reagent A and 5 ml. of B, mix, and 
allow to stand for 2 hr. at 15° to 20° C. Filter in a 
porous-bottomed porcelain filtering crucible, the tare 
weight of which is known, using C in a wash bottle 
to make the transfer. Wash 10 times with C and 5 times 
with 2-ml. portions of D. Aspirate until quite dry, 
Wipe the outside with a cloth, dry for 1 hr. at 105° C, 
cool in a desiccator, and weigh. 

Modified Procedure 

For very small quantities of potassium (0.2 meq./l. 
or less) . Evaporate 200 ml. of the sample in a plati- 
num dish and remove silica as under Method 76a. This 
aliquot may be used for the determination of dissolved 
solids as under Method 74 and silica as under Method 
76a. After removal of silica, evaporate the filtrate to 
dryness to remove hydrochloric acid, add 10 ml. of 
water, 1 ml. of reagent A, and 5 ml. of B, and put the 
sample in the refrigerator at 5° to 15° C. overnight. 
When gypsum is high, add more of the reagents (10 
ml. of water, 1 ml. of A, and 5 ml. of B for each 5 
meq./l. of gypsum present) . The following morning, 
remove the samples from the refrigerator, filter 
through a porous-bottomed porcelain crucible, and 
proceed as directed above. 

If the sample is high in organic matter, such as a 
sewage effluent, evaporate the filtrate to dryness, take 
up in aqua regia (3 parts cone, hydrochloric acid + 1 
part cone, nitric acid), and evaporate again before 
potassium is precipitated. 

The composition of the precipitate can be represented 
by the formula K 2 NaCo(N0 2 ) 6 H 2 0. K- 17.216 per- 
cent. 

Calculations 

Milliequivalents per liter of K = gm. di-potassium 
sodium cobaltinitrite precipitate X 4,403. 4/ml. in 
aliquot. 



Reference 

Wilcox (1937). 

(81b) Potassium by Cobaltinitrite, Volu- 
metric 

Reagents 

In addition to the reagents listed under the gravi- 
metric procedure, except 95 percent ethyl alcohol, the 
following are required: 

A. Sodium hydroxide, approximately 0.5 N. 

B. Sulfuric acid, cone. 

C. Potassium permanganate solution, standard 
0.05 N. 

D. Sodium oxalate solution, standard 0.05 N. 

Procedure 

Follow the gravimetric procedure of Method 81a 
through the precipitation and washing with nitric acid. 
Omit washing with alcohol. Wash the precipitate into 
a 250-ml. beaker, place the crucible in the beaker, and 
make to about 100 ml. with water. Add 20 ml. of 
reagent A and boil for 3 min. Withdraw into another 
beaker a slight excess of C, make to 50 ml. with water, 
and add 5 ml. of B. Pour the hot potassium cobal- 
tinitrite solution into the cold potassium permanganate 
solution, transfer the crucible, and wash the beaker 
with a small quantity of water. Add an excess of D, 
heat to boiling, and complete the titration with potas- 
sium permanganate. 

Calculations 

Milliequivalents per liter of K = normality of KMn0 4 
X (ml. KMn0 4 -blank) X 181.81/ml. in aliquot. 

Reference 

Wilcox (1937). 

(81c) Potassium by Flame Photometer 

Procedure 

See Method 11a. 

( 82 ) Carbonate and Bicarbonate 

Reagents 

A. Phenolphthalein, 0.25 percent solution in 50 
percent alcohol. 

B. Sulfuric acid, standard 0.050 N. 

C. Methyl orange, 0.1 percent in water. 

Procedure 

Take an aliquot of the sample containing not more 
than 1.0 meq. of carbonate plus bicarbonate and dilute 



146 



AGRICULTURE HANDBOOK 60, U. S. DEPT. OF AGRICULTURE 



to 50 ml., if less than that volume. Add a few drops of 
reagent A, and, if a pink color is produced, titrate with 
B, adding a drop every 2 or 3 seconds until the pink 
color disappears. To the colorless solution from this 
titration or to the original solution, if no color is pro- 
duced with phenolphthalein, add 1 or 2 drops of C, 
continue the titration (without refilling the buret) to 
the methyl orange end point, and note the total reading. 
(Reserve the solution for the determination of chloride.) 
Blank determinations should be run with the reagents 
and carbon dioxide-free distilled water and corrections 
made, if necessary. 

Remarks 

To facilitate calculations a table similar to that 
shown in APHA Standard Methods (1946) is included 
(table 18). 

Table 18— The titration of hydroxide, carbonate, and 
bicarbonate ions in the presence of phenolphthalein 
and methyl orange indicators. 



Result of titration l 


Titration value related to 
each ion — 




Hydrox- 
ide 


Carbon- 
ate 


IP 
IP 

2 (T-P) 



Bicar- 
bonate 


P=0 

P<U T 





2P-T 
T 


T 
T-2P 


p=^y, t 





pyyiT 

P=T 







^—Titration to the phenolphthalein end point; T=total 
titration to the methyl end point. 

Calculations 

Ion sought, milliequivalents per liter of either OH, 
C0 3 , or HC0 3 = 1000 X normality of the acid X [titra- 
tion value (from table 18) in ml. acid — blank] /ml. in 
aliquot. 

References 

American Public Health Association and American 
Water Works Association (1946, p. 9), Association of 
Official Agricultural Chemists (1950, 31. 18, p. 539). 

(83) Sulfate 

Reagents 

A. Hydrochloric acid, cone. 

B. Barium chloride solution, 10 percent. Dissolve 
100 gm. BaCl 2 *2H 2 in 1 liter of water and filter. 

C. Methyl orange, 0.1 percent in water. 



Procedure 

Take an aliquot of the sample containing between 
0.2 and 5 meq. of sulfate and, if necessary, dilute to a 
volume of approximately 200 ml. Add a few drops of 
reagent C and 1 ml. of A. Heat to boiling and add an 
excess of B drop by drop with constant stirring. Allow 
to stand on the water bath until the volume is reduced 
to about 50 ml. After cooling, the precipitate of barium 
sulfate is filtered through an ashless filter paper and 
washed with water until free from chloride. The filter 
paper is then carefully folded, placed in a tared por- 
celain or silica crucible, ignited in a well-ventilated 
muffle at low red heat, and weighed. 

Calculations 

Milliequivalents per liter of S0 4 = gm. BaS0 4 X 
8568.2/ml. in aliquot. 

Reference 

Association of Official Agriculture Chemists (1950, 
31.27, p. 541). 

(84) Chloride 

Reagents 

A. Potassium chromate indicator. Dissolve 5 gm. 
of potassium chromate in water and add a saturated 
solution of silver nitrate until a slight permanent red 
precipitate is produced; filter and dilute to 100 ml. 

B. Standard silver nitrate solution, 0.05 N. Dissolve 
8.4944 gm. silver nitrate in water and dilute to 1 liter. 
Check by titration against pure sodium chloride or 
standard potassium chloride (reagent A, Method 72). 

Procedure 

To the solution from the carbonate and bicarbonate 
determination (Method 82), add 1 ml. of reagent A 
and titrate with B. Correct for the quantity of silver 
nitrate solution necessary to give, in 50 ml. of chloride- 
free water with 1 ml. potassium chromate indicator, 
the shade obtained at the end of the titration of the 
sample. 

If the size of aliquot that is suitable for the carbonate- 
bicarbonate titration is too large for the chloride de- 
termination, a smaller aliquot must be taken and neu- 
tralized to methyl orange. The aliquot should contain 
not more than 2 meq. of chloride. 

Calculations 

Milliequivalents per liter of CI = 1000 X normality of 
the AgN0 3 X(ml. AgN0 3 ~ blank) /ml. in aliquot. 

Reference 

Association of Official Agricultural Chemists (1950, 
31.10, p. 536). 



SALINE AND ALKALI SOILS 



147 



(85) Fluoride 

Remarks 

Method suggested is given in Standard Methods, 
APHA (1946^, substituting sulfuric acid for perchloric 
acid and silver sulfate for silver perchlorate. 

It has been found reliable for potable waters of ordinary com- 
position. Up to the following limits expressed as parts per 
million it is not interfered with by: Chloride ion (CI)— 500 
ppm., sulfate ion (SO* )— 200 ppm., alkalinity (expressed as 
CaC0 3 )— 200 ppm., acidity (expressed as CaC0 3 )— 200 ppm., 
iron (Fe) — 2 ppm., aluminum (Al) — 0.5 ppm., phosphate ion 
(P0 4 )— 1 ppm., color 25, turbidity 25. 

If limits are exceeded, separate fluoride by distillation. 

Reagents 

A. Acid zirconium alizarin reagent. Dissolve 0.3 
gm. zirconium oxychloride (ZrOCl 2 *8H 2 0) in 50 ml. 
distilled water contained in a 1-liter glass-stoppered 
flask. Dissolve 0.07 gm. alizarin sodium monosulfo- 
nate in 50 ml. distilled water and pour slowly into the 
zirconium oxychloride solution, while swirling the flask. 
This solution clears on standing for a few minutes. 
Prepare a mixed acid solution as follows: Dilute 112 
ml. cone, hydrochloric acid to 500 ml. with distilled 
water. Dilute 37 ml. cone, sulfuric acid to 500 ml. 
with distilled water. After cooling, mix the two acids. 
To the zirconium alizarin solution in the 1-liter flask, 
add the mixed acid solution to the mark and mix. The 
reagent changes in color from red to yellow within an 
hour and is then ready for use. If stored in a refrigera- 
tor, it may be used for 60 to 90 days. 

B. Standard sodium fluoride solution. Dissolve 
0.221 gm. sodium fluoride in distilled water and make 
up to 1 liter. Dilute 100 ml. of the stock sodium 
fluoride solution to 1 liter with distilled water. One 
ml. is equivalent to 0.01 mg. of fluoride. 

Procedure 

To 100 ml. of sample containing not more than 0.14 
mg. fluoride and to standards made up to 100 ml. with 
distilled water, contained in 100-ml. matched Nessler 
tubes, add 5 ml. of reagent A, accurately measured from 
a 5-ml. volumetric pipet. Mix and compare sample 
with standards after standing 1 hr. at room tempera- 
ture. Recommended standards are 0, 0.01, 0.02, 0.03, 
0.04, 0.05, 0.06, 0.08, 0.10, 0.12, and 0.14 mg. of 
fluoride. Since the color of the zirconium-alizarin lake 
varies with temperature, samples and standards should 
have the same temperature within 1° or 2° C, before 
adding the reagent. 

Calculations 

Parts per million F=mg. FXl,000/ml. in aliquot. 

Reference 

American Public Health Association and American 
Water Works Association (1946, 39A-2, p. 76, and 
39B-2,p.77). 



(86) Nitrate 

(86a) Nitrate, Phenoldisulfonic Acid 

(For water of low chloride content.) 

Procedure 

See Method 15. 

(86b) Nitrate, Devarda 

(For water of high chloride content.) 

Apparatus 

Nitrogen distilling apparatus with scrubber bulbs. 

Reagents 

A. Devarda alloy. 

B. Sodium hydroxide, saturated solution. 

C. Boric acid, 2 percent solution. 

D. Standard sulfuric acid, 0.05 N. 

E. Bromcresol green-methyl red (BCG— MR) indi- 
cator solution. 20 Prepare a 0.1 percent bromcresol 
green solution, adding 2 ml. 0.1 N sodium hydroxide 
per 0.1 gm. of indicator. Prepare a 0.1 percent methyl 
red solution in 95 percent ethyl alcohol, adding 3 ml. 
0.1 N sodium hydroxide per 0.1 gm. of indicator. Mix 
75 ml. bromcresol green, 25 ml. methyl red, and 100 ml. 
of 95 percent ethyl alcohol. The indicator should be 
gray in a solution containing boric acid and ammonium 
sulfate in concentrations equal to those encountered in 
the Devarda procedure. It is often necessary to add a 
little of one or the other of the indicators until the 
proper shade is obtained. The color change is from 
green in alkali through gray at the end point to red in 
acid solution. 

Procedure 

Place 50 ml. of the sample, or such volume as will 
contain not less than 0.2 meq. nitrate, in a Kjeldahl 
flask and add 2 gm. Devarda alloy. Make up to 300 
ml. with distilled water, then add 2 ml. of reagent B, 
allowing it to run down the side of the flask so that it 
does not mix with the contents at once. Connect with 
the distilling apparatus and rotate the flask to mix. 
Heat slowly at first and then at such a rate that the 
200 ml. of distillate required will pass over in 1 hr. 
Collect the distillate in 50 ml. of C. The ammonia is 
titrated with D, using indicator E. 

Calculations 

Milliequivalents per liter of N0 3 = 1,000 X normality 
of acidX (ml. acid — blank) /ml. in aliquot. 

Reference 

Association of Official Agricultural Chemists (1950, 
2.30, p. 14). 



20 



Chapman, H. D. Private communication. 



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DONNAN, W. W., AND CHRISTIANSEN, J. E. 

1944. ground water determinations. West. Construct. 
News 19 (11) : 77-79, illus. 
Dorph-Petersen, K., and Steenbjerg, F. 

1950. investigations of the effect of fertilizers con- 
taining sodium. Plant and Soil 2: 283-300, illus. 
Dyal, R. S., and Hendricks, S. B. 

1950. total surface of clays in polar liquids as a 
characteristic index. Soil Sci. 69: 421-^132, illus. 

and Hendricks, S. B. 

1952. formation of mixed layer minerals by potassium 
fixation in montmorillonite. Soil Sci. Soc. 
Amer. Proc. 16 : 4S--48, illus. 



Eaton, F. M. 

1935. boron in soils and irrigation waters and its ef- 
fect on plants with particular reference to the 

SAN JOAQUIN VALLEY OF CALIFORNIA. U. S. Dept. 

Agr. Tech. Bui. 448, 131 pp., illus. 



1942. TOXICITY AND ACCUMULATION OF CHLORIDE AND SUL- 
FATE salts in plants. Jour. Agr. Res. 64: 357-399, 
illus. 



1944. DEFICIENCY, TOXICITY, AND ACCUMULATION OF BORON 

in plants. Jour. Agr. Res. 69: 237-277, illus. 



1950. SIGNIFICANCE OF CARBONATES IN IRRIGATION WATERS. 

Soil Sci. 69: 123-133. 
and Wilcox, L. V. 



1939. THE BEHAVIOR OF BORON IN SOILS. U. S. Dept. Agr. 

Tech. Bui. 696, 57 pp., illus. 

Fireman, M. 

1944. permeability measurements on disturbed soil 
samples. Soil Sci. 58: 337-353, illus. 

and Hayward, H. E. 

1952. indicator significance of some shrubs in the 
escalante desert, utah. Bot. Gaz. 114: 143-155, 
illus. 

AND WADLEIGH, C. H. 



1951. A statistical study of the relation BETWEEN pH 

AND THE EXCHANGEABLE-SODIUM-PERCENTAGE OF 

western soils. Soil Sci. 71 : 273-285, illus. 

Flowers, S. 

1934. vegetation of the great salt lake region. Bot. 
Gaz. 95 : 353^18, illus. 
Frevert, R. K., and Kirkham, D. 

1949. A FIELD METHOD FOR MEASURING THE PERMEABILITY 

of soil below a water table. Highway Res. Bd. 
Proc. (1948) 28: 433^42, illus. 
Fullmer, F. S. 

1950. metering dry fertilizers and soil amendments 
into irrigation systems. Better Crops With Plant 
Food 34(3) : 8-14, 40-41, illus. 

Gapon, E. N. 

1933. theory of exchange adsorption in soils. Zhur. 
Obshch. Khim. (Jour. Gen. Chem.) 3: 144-152, illus. 
Gardner, R. 

1945. some soil properties related to the sodium salt 
problem in irrigated soils. U. S. Dept. Agr. Tech. 
Bui. 902, 28 pp., illus. 
Gauch, H. G., and Wadleigh, C. H. 

1951. the salt tolerance and chemical composition of 
rhodes and dallis grasses grown in sand culture. 
Bot. Gaz. 112: 259-271, illus. 

Gedroiz, K. K. 

1917. SALINE SOILS AND THEIR IMPROVEMENT. Zhur. Opytn. 

Agron. (Jour. f. Expt. Landw.) 18: 122-140. [In 
Russian. French summary, pp. 138-140.3 [Trans- 
lated by S. A. Waksman.] 
Guggenheim, E. A. 

1945. STATISTICAL THERMODYNAMICS OF MIXTURES WITH 

zero energies of mixing. Roy. Soc. London Proc, 
Ser. A., 183: 203-213. 
Haas, A. R. C. 

1950. EFFECT OF SODIUM CHLORIDE ON MEXICAN, GUATE- 
MALAN AND WEST INDIAN AVOCADO SEEDLINGS. Calif. 

Avocado Soc. Yearbook 1950: 153-160, illus. 
Harley, C. P., and Lindner, R. C. 

1945. OBSERVED RESPONSES OF APPLE AND PEAR TREES TO 
SOME IRRIGATION WATERS OF NORTH CENTRAL WASH- 
INGTON. Amer. Soc. Hort. Sci. Proc. 46: 35^44, illus. 
Harmer, P. M., and Benne, E. J. 

1941. EFFECTS OF APPLYING common salt to a muck soil 
on the yield, composition, and quality of certain 
vegetable crops and on the composition of the 
soil producing them. Amer. Soc. Agron. Jour. 
33: 952-979, illus. 



150 



AGRICULTURE HANDBOOK 60, U. S. DEPT. OF AGRICULTURE 



Harper, H. J. 

1946. EFFECT OF CHLORIDE ON PHYSICAL APPEARANCE AND 
CHEMICAL COMPOSITION OF LEAVES ON PECANS AND 
OTHER NATIVE OKLAHOMA TREES. Okla. Agr. Expt. 

Sta. Tech. Bui. 23, 30 pp., illus. 
Harris, F. S. 

1920. SOIL ALKALI, ITS ORIGIN, NATURE, AND TREATMENT. 

258 pp., illus. New York and London. 
Harris, J. A. 

1925. A TABLE TO FACILITATE CORRECTION FOR UNDERCOOLING 

in cryoscopic work. Amer. Jour Bot. 12: 499-501. 

AND GORTNER, R. A. 

1914. NOTES ON THE CALCULATION OF THE OSMOTIC PRESSURE 
OF EXPRESSED VEGETABLE SAPS FROM THE DEPRESSION 
OF THE FREEZING POINT, WITH A TABLE FOR THE VALUES 

of p for A — o.ooi to A — 2.909°. Amer. Jour. 
Bot. 1: 75-78. 
Gortner, R. A., Hoffman, W. F., and others. 



1924. the osmotic concentration, specific electrical 
conductivity, and chloride content of the tissue 
fluids of the indicator plants of tooele valley, 
Utah. Jour. Agr. Res. 27: 893-924. . 
Hatcher, J. T., and Wilcox, L. V. 

1950. COLORIMETRIC DETERMINATION OF BORON USING CAR- 
MINE. Analyt. Chem. 22: 567-569, illus. 
Hayward, H. E., Long, E. M., and Uhvits, R. 

1946. THE EFFECT OF CHLORIDE AND SULFATE SALTS ON THE 
GROWTH AND DEVELOPMENT OF THE ELBERTA PEACH ON 
SHALIL AND LOVELL ROOTSTOCKS. U. S. Dept. Agr. 

Tech. Bui. 922, 48 pp., illus. 

AND MAGISTAD, O. C. 

1946. THE SALT PROBLEM IN IRRIGATION AGRICULTURE. U. S. 

Dept. Agr. Misc. Pub. 607, 27 pp., illus. 
and Spurr, W. B. 



1944. EFFECTS OF ISOSMOTIC CONCENTRATIONS OF INORGANIC 
AND ORGANIC SUBSTRATES ON THE ENTRY OF WATER 

into corn roots. Bot. Gaz. 106: 131-139, illus. 

AND WADLEIGH, C. H. 



1949. plant growth on saline and alkali soils. Ad- 
vances in Agron. 1 : 1-38, illus. 

Heald, W. R., Moodie, C. D., and Leamer, R. W. 

1950. leaching and pre-emergence irrigation for sugar 
beets on saline soils. Wash. Agr. Expt. Sta. Bui. 
519, 16 pp., illus. 

Hellman, N. N., and McKelvey, V. E. 

1941. A hydrometer-pipette method for mechanical 
analysis. Jour. Sedimentary Petrology 11 : 3-9, 
illus. 
Hilgard, E. W. 

1906. soils, their formation, properties, composition, 
and relations to climate and plant growth. 593 
pp., illus. New York and London. 
Hissink, D. J. 

1933. DIE SALZTONBODEN UND DIE ALKALITONBODEN IN DEN 

niederlanden. Internatl. Soc. Soil Sci. 2nd Com. 
(Copenhagen), Part A: 185-189. 

HOOGHOUDT, S. B. 

1936. BIJDRAGEN TOT DE KENNIS VAN EENIGE NATUURKUNDIGE 

grootheden van der grond, no. 4. [Netherlands] 
Dir. van den Landbouw, Verslag. van Landbouwk. 
Onderzoek.42 (13) B : 449-541, illus. 



1952. tile drainage and subirrigation. Soil Sci. 74: 
35-48, illus. 
Iljin, W. S. 

1951. metabolism of plants affected with lime-induced 
CHLOROSIS (CALCIOSE) II. organic acids and carbo- 
hydrates. Plant and Soil 3: 339-351, illus. 



1952. metabolism of plants affected with lime-induced 
chlorosis i calciose j iii. mineral elements. 
Plant and Soil 4: 11-28, illus. 

ISRAELSEN, 0. W. 

1950. IRRIGATION PRINCIPLES AND PRACTICES. Ed. 2, 405 

pp., illus. New York. 



Jacob, C. E. 

1940. ON THE FLOW OF WATER IN AN ELASTIC ARTESIAN 

aquifer. Amer. Geophys. Union Trans. 1940: 574- 
586, illus. 



1947. DRAWDOWN TEST TO DETERMINE THE EFFECTIVE RADIUS 

of artesian well. Amer. Soc. Civ. Engin. Trans. 
112: 1047-1064, illus. 
Jenny, H., Vlamis, J., and Martin, W. E. 

1950. GREENHOUSE ASSAY OF FERTILITY OF CALIFORNIA SOILS. 

Hilgardia 20 : 1-8, illus. 
Jensen, M. C, Lewis, G. C, and Baker, G. O. 

1951. CHARACTERISTICS OF IRRIGATION WATERS IN IDAHO. 

Idaho Agr. Expt. Sta. Res. Bui. 19, 44 pp., illus. 
Johnson, H. P., Frevert, R. K., and Evans, D. D. 

1952. SIMPLIFIED PROCEDURE FOR MEASUREMENT AND COM- 
PUTATION OF SOIL PERMEABILITY BELOW THE WATER 

table. Agr. Engin. 33 : 283-286, illus. 
Kearney, T. H., Briggs, L. J., Shantz, H. L., and others. 

1914. INDICATOR SIGNIFICANCE OF VEGETATION IN TOOELE 

valley, utah. Jour. Agr. Res. 1: 365-417, illus. 

AND SCOFIELD, C. S. 

1936. THE CHOICE OF CROPS FOR SALINE LAND. U. S. Dept. 

Agr. Cir. 404, 24 pp. 
Kelley, O. J., Hardman, J. A., and Jennings, D. S. 

1948. A SOIL-SAMPLING MACHINE FOR OBTAINING TWO-, 
THREE- AND FOUR-INCH DIAMETER CORES OF UNDIS- 
TURBED SOIL TO A DEPTH OF SIX FEET. Soil Sci. Soc. 

Amer. Proc. (1947) 12: 85-87, illus. 
Kelley, W. P. 

1948. cation exchange in soils. Amer. Chem. Soc. 

Monog. Ser. 109, 144 pp., illus. New York. 



1951. ALKALI SOILS, THEIR FORMATION, PROPERTIES AND 

reclamation. 176 pp., illus. New York. 
and Brown, S. M. 



1934. principles governing the reclamation of alkali 
soils. Hilgardia 8: 149-177, illus. 
Kilmer, V. J., and Alexander, L. T. 

1949. METHODS OF MAKING MECHANICAL ANALYSIS OF SOILS. 

Soil. Sci. 68: 15-24. 
Kirkham, D. 

1946. PROPOSED METHOD FOR FIELD MEASUREMENT OF PER- 
MEABILITY OF SOIL BELOW THE WATER TABLE. Soil 

Sci. Soc. Amer. Proc. (1945) 10: 58-68, illus. 



1947. FIELD METHOD FOR DETERMINATION OF AIR PERMEA- 
BILITY OF SOIL IN ITS UNDISTURBED STATE. Soil Sci. 

Soc. Amer. Proc. (1946) 11: 93-99, illus. 

1948. REDUCTION IN SEEPAGE TO SOIL UNDERDRAINS RESULT- 
ING FROM THEIR PARTIAL EMBEDMENT IN, OR PROX- 
IMITY TO, AN IMPERVIOUS SUBSTRATUM. Soil Sci. SoC. 

Amer. Proc. (1947) 12: 54-59, illus. 



1949. FLOW OF PONDED WATER INTO DRAIN TUBES IN SOIL 

overlying an impervious layer. Amer. Geophys. 
Union Trans. 30: 369-385, illus. 
and Bavel, C. H. M. van. 



1949. theory of seepage into auger holes. Soil Sci. 
Soc. Amer. Proc. (1948) 13: 75-82, illus. 
Kitson, R. E., and Mellon, M. G. 

1944. COLORIMETRIC DETERMINATION OF PHOSPHORUS AS 

molybdivanadophosphoric acid. Indus, and Engin. 
Chem., Analyt. Ed. 16: 379-383, illus. 
Krishnamoorthy, C, and Overstreet, R. 

1950. AN EXPERIMENTAL EVALUATION OF ION-EXCHANGE RE- 
LATIONSHIPS. Soil Sci. 69: 41-53. 
Lehr, J. J. 

1942. THE IMPORTANCE OF SODIUM FOR PLANT NUTRITION. 
III. THE EQUILIBRIUM OF CATIONS IN THE BEET. Soil 

Sci. 53: 399-411, illus. 



1949. EXPLORATORY POT EXPERIMENTS ON SENSITIVENESS OF 
DIFFERENT CROPS TO SODIUM. A. SPINACH. Plant 

and Soil 2 : 37-48, illus. 



SALINE AND ALKALI SOILS 



151 



LlLLELAND, 0., BROWN, J. G., AND SwANSON, C. 

1945. RESEARCH SHOWS EXCESS SODIUM MAY CAUSE LEAF TIP 

burn. Almond Facts 9 (2) : 1, 5, ill us. 

LUTHIN, J. N., AND KlRKHAM, D. 

1949. A PIEZOMETER METHOD FOR MEASURING PERMEABILITY 
OF SOIL IN SITU BELOW A WATER TABLE. Soil Sci. 

68 : 349-358, illus. 
McGeorge, W. T. 

1949. A STUDY OF LIME-INDUCED CHLOROSIS IN ARIZONA 

orchards. Ariz. Agr. Expt. Sta. Tech. Bui. 117, pp. 
341-388, illus. 

AND BREAZEALE, J. F. 

1938. STUDIES ON SOIL STRUCTURE: EFFECT OF PUDDLED 

soils on plant growth. Ariz. Agr. Expt. Sta. Tech. 
Bui. 72, pp. 413-447, illus. 

AND BREAZEALE, E. L. 



1951. ABSORPTION OF GYPSUM BY SEMIARID SOILS. Ariz. 

Agr. Expt. Sta. Tech. Bui. 122, pp. 1-49, illus. 
— and Greene, R. A. 



1935. oxidation of sulphur in Arizona soils and its 
effect on soil properties. Ariz. Agr. Expt. Sta. 
Tech. Bui. 59, pp. 297-325, illus. 

Magistad, O. C. 

1945. plant growth relations on saline and alkali 
soils. Bot. Rev. 11: 181-230. 

and Christiansen, J. E. 

1944. SALINE soils, their nature and management. 
U. S. Dept. Agr. Cir. 707, 32 pp., illus. 

Marsh, A. W., and Swarner, L. R. 

1949. the collection and study of natural soil cores 

FOR DETERMINING IRRIGATION PROPERTIES. Soil Sci. 

Soc. Amer. Proc. (1948) 13: 515-518. 
Martin, W. P., Taylor, G. S., Engibous, J. C, and Burnett, E. 

1952. SOIL AND CROP RESPONSES FROM FIELD APPLICATIONS 

of soil conditioners. Soil Sci. 73: 455-471, illus. 

Masaewa, M. 

1936. zur frage der chlorophobie der pflanzen. Bodenk. 
u. Pflanzenernsir. 1:39-56. 

Mattson, S., and Wiklander, L. 

1940. the laws of colloidal behavior: xxi. a. the 
amphoteric points, the pH, and the donnan 
equilibrium. Soil Sci. 49: 109-134, illus. 

Middleton, H. E. 

1930. properties of soils which influence soil erosion. 
U. S. Dept. Agr. Tech. Bui. 178, 16 pp. 

Miller, M. R. 

1950. the quality of the water of the humboldt 
river. Nev. Agr. Expt. Sta. Bui. 186, 31 pp. 

Mortland, M. M., and Gieseking, J. E. 

1951. influence of the silicate ion on potassium fixa- 
tion. Soil Sci. 71 : 381-385. 

musgrave, g. w. 

1935. the infiltration capacity of soils in relation to 
the control of surface runoff and erosion- 
Amer. Soc. Agron. Jour. 27 : 336-345, illus. 
National Research Council. 

1929. international critical tables of numerical data, 

PHYSICS, CHEMISTRY AND TECHNOLOGY. vol. 6, 471 

pp., illus. New York. 

Peech, M., Alexander, L. T., Dean, L. A., and Reed, J. F. 
1947. methods of soil analysis for SOIL-FERTILITY IN- 
VESTIGATIONS. U. S. Dept. Agr. Cir. 757, 25 pp. 

Peterson, D. F., Jr., Israelson, 0. W., and Hansen, V. E. 

1952. hydraulics of wells. Utah Agr. Expt. Sta. Tech. 
Bui. 351, 48 pp., illus. 

Pillsbury, A. F., and Christiansen, J. E. 

1947. installing ground-water piezometers by jetting 
for drainage investigations in coachella valley, 
California. Agr. Engin. 28: 409^10, illus. 

Ratner, E. 1. 

1935. the influence of exchangeable sodium in the soil 
on its properties as a medium for plant growth. 
Soil Sci. 40: 459-471, illus. 



Ratner, E. I. 

1944. physiological effect of alkalinity of soils 

and the ameliorative role of plant root systems 

on SOLONETZ (ALKALI SOILS). pochvovedenie. 

(pedology) : 205-227, illus. [In Russian. English 

summary, pp. 226-227.] 
Ravikovitch, S., and Bidner, N. 

1937. the deterioration of grape-vines in saline soils. 

Empire Jour. Expt. Agr. 5: 197-203, illus. 
Reed, H. S., and Haas, A. R. C. 

1924. nutrient and toxic effects of certain ions on 

citrus and walnut trees with special reference 

to the concentration AND pH OF THE medium. 

Calif. Agr. Expt. Sta. Tech. Paper 17, 75 pp., illus. 
Reeve, R. C, Allison, L. E., and Peterson, D. F., Jr. 

1948. reclamation of saline-alkali soils by leaching — 
delta area, utah. Utah Agr. Expt. Sta. Bui. 335, 
52 pp., illus. 

and Jensen, M. C. 

1949. piezometers for ground-water flow studies and 
measurement of subsoil permeability. Agr. 
Engin. 30: 435-438, illus. 

and Kirkham, D. 



1951. soil anisotropy and some field methods for 
measuring permeability. Amer. Geophys. Union 
Trans. 32 : 582-590, illus. 
Reger, J. S., Pillsbury, A. F., Reeve, R. C, and Petersen, 
R. K. 

1950. TECHNIQUES FOR DRAINAGE INVESTIGATIONS IN THE 

coachella valley, California. Agr. Engin. 31: 
559-564, illus. 
Reitemeier, R. F. 

1943. semimicroanalysis of saline soil solutions. 
Indus, and Engin. Chem., Analyt. Ed. 15: 393-402, 
illus. 



1946. EFFECT OF MOISTURE CONTENT ON THE DISSOLVED AND 
EXCHANGEABLE IONS OF SOILS OF ARID REGIONS. Soil 

Sci. 61 : 195-214, illus. 

— Christiansen, J. E., Moore, R. E., and Aldrich, W. W. 

1948. EFFECT OF GYPSUM, ORGANIC MATTER AND DRYING ON 
INFILTRATION OF A SODIUM WATER INTO A FINE SANDY 

loam. U. S. Dept. Agr. Tech. Bui. 937, 36 pp., 
illus. 

— and Fireman, M. 



1944. PREVENTION OF CALCIUM CARBONATE PRECIPITATION IN 
SOIL SOLUTIONS AND WATERS BY SODIUM HEXAMETA- 

phosphate. Soil Sci. 58: 35-41, illus. 
— and Richards, L. A. 

1944. RELIABILITY OF THE PRESSURE-MEMBRANE METHOD 
FOR EXTRACTION OF SOIL SOLUTION. Soil Sci. 57: 

119-135, illus. 
and Wilcox, L. V. 



1946. A CRITIQUE OF ESTIMATING SOIL SOLUTION CONCEN- 

TRATION FROM THE ELECTRICAL CONDUCTIVITY OF 

saturated soils. Soil Sci. 61: 281-293, illus. 
Richards, L. A. ' 

1947. PRESSURE-MEMBRANE APPARATUS CONSTRUCTION AND 

use. Agr. Engin. 28: 451-454, 460, illus. 



1948. POROUS PLATE APPARATUS FOR MEASURING MOISTURE 
RETENTION AND TRANSMISSION BY SOIL. Soil Sci. 

66: 105-110, illus. 



1949a. FILTER FUNNELS FOR SOIL EXTRACTS. Agron. Jour. 

41 : 446, illus. 



1949b. METHODS FOR MOUNTING POROUS PLATES USED IN 

soil moisture measurements. Agron. Jour. 41: 
489, illus. 



1952. WATER CONDUCTING AND RETAINING PROPERTIES OF 

soils in relation to irrigation. Internatl. Sym- 
posium on Desert Res. Proc, pp. 1-22, illus. (Res. 
Council of Israel in coop, with UNESCO.) 



152 



AGRICULTURE HANDBOOK 60, U. S. DEPT. OF AGRICULTURE 



Richards, L. A., and Campbell, R. B. 

1948. USE OF THERMISTORS FOR MEASURING THE FREEZING 

POINT OF SOLUTIONS AND soils. Soil Sci. 65: 429- 
436, illus. 
and Campbell, R. B. 

1949. THE FREEZING POINT OF MOISTURE IN SOIL CORES. Soil 

Sci. Soc. Amer. Proc. (1948) 13: 70-74, illus. 

AND WADLEIGH, C. H. 

1952. soil water and plant growth. In Soil Physical 
Conditions and Plant Growth. Byron T. Shaw, Ed., 
491 pp., illus. New York. 
and Weaver, L. R. 



1944. MOISTURE RETENTION BY SOME IRRIGATED SOILS AS RE- 
LATED TO SOIL-MOISTURE TENSION. Jour. Agr. ReS. 

69: 215-235, illus. 
Roberts, R. C. 

1950. CHEMICAL EFFECTS OF SALT-TOLERANT SHRUBS ON 

soils. Fourth Internatl. Cong. Soil Sci. Trans. 
1: 404-406. 
Russell, M. B, 

1949. METHODS OF MEASURING SOIL STRUCTURE AND AERA- 
TION. Soil Sci. 68: 25-35. 
Sampson, A. W. 

1939. PLANT INDICATORS — CONCEPT AND STATUS. Bot. Rev. 

5: 155-206, illus. 

SCHOFIELD, R. K. 

1947. A RATIO LAW GOVERNING THE EQUILIBRIUM OF CATIONS 

in the soil solution. Internatl. Cong. Pure and 
Appl. Chem. (London) Proc. (11) 3: 257-261, 
illus. 

AND BOTELHODA COSTA, J. V. 

1938. THE MEASUREMENT OF pF IN SOIL BY FREEZING-POINT. 

Jour. Agr. Sci. [Englandl 28: 644-653, illus. 

SCHOLLENBERGER, C. J. 

1945. DETERMINATION OF CARBONATES IN SOIL. Soil Sci. 

59: 57-63, illus. 

SCOFIELD, C. S. 

1936. THE SALINITY OF IRRIGATION WATER. Smithsn. Inst. 

Ann. Rpt, 1935: 275-287, illus. 



1940. SALT BALANCE IN IRRIGATED AREAS. Jour. Agr. Res. 

61: 17-39, illus. 

AND HEADLEY, F. B. 

1921. QUALITY OF IRRIGATION WATER IN RELATION TO LAND 

reclamation. Jour. Agr. Res. 21: 265-278. 

SCHANTZ, H. L., AND PlEMEISAL, R. L. 

1924. INDICATOR SIGNIFICANCE OF THE NATURAL VEGETATION 
OF THE SOUTHWESTERN DESERT REGION. Jour. Agr. 

Res. 28: 721-802, illus. 

SlGMOND, A. A. J. DE. 

1924. THE ALKALI SOILS IN HUNGARv AND THEIR RECLAMA- 
TION. Soil Sci. 18:379-381. 



1928. THE CLASSIFICATION OF ALKALI AND SALTY SOILS. 

First Internatl. Cong. Soil Sci. Proc. (1927) 1: 330- 
344, illus. 



1938. THE PRINCIPLES OF SOIL SCIENCE. 362 pp., illus. 

London. 
Smith, H. V. 

1949. BORON AS A FACTOR IN ARIZONA'S AGRICULTURE. Ariz. 

Agr. Expt. Sta. Tech. Bui. 118, pp. 391-435, illus. 

Caster, A. B., Fuller, W. H., and others. 

1949. the chemical composition of representative ARI- 
ZONA waters. Ariz. Agr. Expt. Sta. Bui. 225, pp. 
1-76, illus. 

Snell, F. D., and Snell, C. T. 

1936. COLORIMETRIC METHODS OF ANALYSIS. Ed. 2, V. 1, 

illus. New York. 
Soil Science Society of America. 

1952. REPORT OF subcommittee on permeability and in- 
filtration, committee on terminolocy. Soil Sci. 
Soc. Amer. Proc. 16: 85-88. 
Soil Survey Staff. 

1951. soil survey manual. U. S. Dept. Agr. Handb. No. 
18. 503 pp., illus, Washington. 



Stewart, G., Cottam, W. P., and Hutchings, S. S. 

1940. INFLUENCE OF UNRESTRICTED GRAZING ON NORTHERN 
SALT DESERT PLANT ASSOCIATIONS IN WESTERN UTAH. 

Jour. Agr. Res. 60: 289-316, illus. 

Tanner, C. B., and Jackson, M. L. 

1948. nomocraphs of sedimentation times for soil 
particles under gravity or centrifugal accelera- 
tion. Soil Sci. Soc. Amer. Proc. (1947) 12: 60-65, 
illus. 

Teakle, L. J. H. 

1937. THE SALT (SODIUM CHLORIDE) CONTENT OF RAIN- 
WATER. West. Austral. Dept. Agr. Jour., Ser. 2, 14:' 
115-123, illus. 
Theis, C. V. 

1935. THE RELATION BETWEEN THE LOWERING OF THE 
PIEZOMETRIC SURFACE AND THE RATE AND DURATION OF 
DISCHARGE OF A WELL USING GROUND- WATER STORAGE. 

Amer. Geophys. Union Trans. 16: 519-524, illus. 
Thomas, J. E. 

1934. THE DIAGNOSTIC VALUE OF THE CHLORINE CONTENT OF 

the vine leaf. Austral. Council Sci. & Indus. Res., 
Jour. 7: 29-38, illus. 
Thorne, D. W. 

1945. GROWTH AND NUTRITION OF TOMATO PLANTS AS IN- 
FLUENCED BY EXCHANGEABLE SODIUM, CALCIUM, AND 

potassium. Soil Sci. Soc. Amer. Proc. (1944) 9: 
185-189, illus. 

Wann, F. B., and Robinson, W. 

1951. HYPOTHESES CONCERNING LIME-INDUCED CHLOROSIS. 

Soil Sci. Soc. Amer. Proc. (1950) 15: 254-258. 
Thorne, J. P., and Thorne, D. W. 

1951. THE IRRIGATION WATERS OF UTAH. Utah. Agr. Expt. 

Sta. Bui. 346, 64 pp., illus. 
Toth, S. J., Prince, A. L., Wallace, A., and Mikkelsen, D. S. 

1948. RAPID QUANTITATIVE DETERMINATION OF EIGHT MIN- 
ERAL ELEMENTS IN PLANT TISSUE BY A SYSTEMATIC 
PROCEDURE INVOLVING USE OF A FLAME PHOTOMETER. 

Soil Sci. 66: 459-466. 
Tyner, E. H. 

1940. THE USE OF SODIUM METAPHOSPHATE FOR DISPERSION 
OF SOILS FOR MECHANICAL ANALYSIS. Soil Sci. SoC. 

Amer. Proc. (1939) 4: 106-113. 
United States Bureau of Reclamation. 

1948. land classification report. Wellton-Mohawk Di- 
vision, Gila Project, Arizona. 32 pp., illus. [Proc- 
essed.] 

United States Geological Survey. 

1945. quality of surface waters of the united states, 
i:>4;t. U. S. Geol. Survey Water-Supply Paper 970, 
180 pp. 







1949. QUALITY OF SURFACE WATERS OF THE UNITED STATES, 

i!U5. U. S. Geol. Survey Water-Supply Paper 1030, 
335 pp. 



i 



1950. QUALITY OF SURFACE WATERS OF THE UNITED STATES, 

line. U. S. Geol. Survey Water-Supply Paper 1050, 
486 pp. 

[United States] National Resources Committee. 

1938. regional planning: part vi — the rio crande joint 
investigation in the upper rio grande basin in 

COLORADO, NEW MEXICO, AND TEXAS. 1936-1937. 

566 pp., illus. Washington. 
[United States] National Resources Planning Board. 

1942. the pecos river joint investigation: reports of 
participating agencies. 407 pp., illus. Washington. 
Veihmeyer, F. J., and Hendrickson, A. H. 

1946. soil density as a factor in determining the perma- 
nent wilting percentage. Soil Sci. 62: 451-456, 
illus. 

and Hendrickson, A. H. 

1948. the permanent wilting percentage as a refer- 
ence for the measuring of soil moisture. Amer. 
Geophys. Union Trans. 29: 887-896, illus. 



i 



■ 1 

i 1 



1 



SALINE AND ALKALI SOILS 



153 



Wadleigh, C. H. 

1946. THE INTEGRATED SOIL MOISTURE STRESS UPON A ROOT 
SYSTEM IN A LARGE CONTAINER OF SALINE SOIL. Soil 

Sci. 61 : 225-238, illus. 

AND AYERS, A. D. 

1945. GROWTH AND BIOCHEMICAL COMPOSITION OF BEAN 
PLANTS AS CONDITIONED BY SOIL MOISTURE TENSION 

and salt concentration. Plant Physiol. 20: 106- 
132, illus. 
and Brown, J. W. 

1952. THE CHEMICAL STATUS OF BEAN PLANTS AFFLICTED 
WITH BICARBONATE-INDUCED CHLOROSIS. Bot. Gaz. 

113: 373-392, illus. 
and Fireman, M. 

1949. SALT DISTRIBUTION UNDER FURROW AND BASIN IRRI- 
GATED COTTON AND ITS EFFECT ON WATER REMOVAL. 

Soil Sci. Soc. Amer. Proc. (1948) 13: 527-530, illus. 

AND GAUCH, H. G. 



1944. THE INFLUENCE OF HIGH CONCENTRATIONS OF SODIUM 
SULFATE, SODIUM CHLORIDE, CALCIUM CHLORIDE, AND 
MAGNESIUM CHLORIDE ON THE GROWTH OF GUAYULE IN 

sand culture. Soil Sci. 58: 399-403, illus. 
Gauch, H. G., and Kolisch, M. 



1951. mineral composition of orchard GRASS GROWN ON 

PACHAPPA LOAM SALINIZED WITH VARIOUS SALTS. Soil 

Sci. 72 : 275-282, illus. 
Walkley, A. 

1935. AN EXAMINATION OF METHODS FOR DETERMINING OR- 
GANIC CARBON AND NITROGEN IN SOILS. Jour. Agr. 

Sci. [England] 25: 598-609, illus. 



1947. A CRITICAL EXAMINATION OF A RAPID METHOD FOR 
DETERMINING ORGANIC CARBON IN SOILS — EFFECT OF 
VARIATIONS IN DIGESTION CONDITIONS AND OF INOR- 
GANIC soil constituents. Soil Sci 63: 251-264, illus. 

Walsh, T., and Clarke, E. J. 

1942. a chlorosis of tomatoes. (Abstract) Eire Dept. 

Agr. Jour. 39: 316-325, illus. 

Wenzel, L. K. 

1942. methods for determining permeability of water- 
bearing materials with special reference to dis- 
charging-well methods. U. S. Geol. Survey Water- 
Supply Paper 887, 192 pp., illus. 



White, L. M., and Ross, W. H. 

1937. influence of fertilizers on the concentration of 
the soil solution. Soil Sci. Soc. Amer. Proc. 
(1936) 1: 181-186, illus. 
Whitney, M., and Briggs, L. J. 

1897. an electrical method of determining the tem- 
perature of soils. U. S. Dept. Agr., Div. Soils Bui. 
7, 15 pp., illus. 
and Means, T. H. 

1897. AN ELECTRICAL METHOD OF DETERMINING THE SOLUBLE 

salt content of soils. U. S. Dept. Agr., Div. Soils 
Bui. 8, 30 pp., illus. 
Wilcox, L. V. 

1932. electrometric titration of boric acid. Indus, and 
Engin. Chem., Analyt. Ed. 4: 38-39. 



1937. determination of potassium by means of an 
aqueous solution of trisodium cobaltinitrite in 
the presence of nitric acid. Indus, and Engin. 
Chem., Analyt. Ed. 9: 136-138. 



1948. the quality of water for irrigation use. U. S. 
Dept. Agr. Tech. Bui. 962, 40 pp., illus. 



1950 electrical conductivity. Amer. Water Works 
Assoc. Jour. 42: 775-776. 



1951. A method for calculating the saturation per- 
centage from the weight of a known volume of 
saturated soil paste. Soil Sci. 72: 233-237, illus. 
Williams, D. E. 

1949. A rapid manometric method for the determina- 
tion of carbonate in soils. Soil Sci. Soc. Amer. 
Proc. (1948) 13: 127-129, illus. 
Williams, W. 0. 

1941. rapid determination of potassium with dipicryla- 
mine. Amer. Soc. Hort. Sci. Proc. 39: 47-50. 
Yoder, R. E. 

1936. a direct method of aggregate analysis of soils 
and a study of the physical nature of erosion 
losses. Amer. Soc. Agron. Jour. 28: 337-351, illus. 
Zuur, A. J. 

1952. DRAINAGE AND RECLAMATION OF LAKES AND OF THE 

Zuiderzee. Soil Sci. 74: 75-89, illus. 



259525 O - 54 - 11 



Glossary 



Absorption. — The process by which a substance is taken into 
and included within another substance, i. e., intake of water 
by soil, or intake of gases, water, nutrients, or other sub- 
stances by plants. 

Adsorption. — The increased concentration of molecules or ions 
at a surface, including exchangeable cations and anions on 
soil particles. 

Aggregate. — A group of soil particles cohering so as to behave 
mechanically as a unit. 

Aggregation. — The act or process of forming aggregates, or 
the state of being aggregated. 

Alkali Soil.— A soil that contains sufficient exchangeable 
sodium to interfere with the growth of most crop plants, either 
with or without appreciable quantities of soluble salts. See 
Nonsaline-Alkali Soil and Saline- Alkali Soil. 

Alkaline. — A chemical term referring to basic reaction where 
the pH reading is above 7, as distinguished from acidic reac- 
tion where the pH reading is below 7. 

Alkaline Soil. — A soil that has an alkaline reaction, i. e., a 
soil for which the pH reading of the saturated soil paste is 
higher than 7. 

Alkalization. — The process whereby the exchangeable-sodium 

content of a soil is increased. 

Atmosphere. — See Standard Atmosphere. 

Base-Exchange Capacity. — See Cation-Exchange-Capacity. 

Bulk Density. — The ratio of the mass of water-free soil to its 
bulk volume. Bulk density is expressed in pounds per cubic 
foot or grams per cubic centimeter and is sometimes referred 
to as "apparent density." When expressed in grams per 
cubic centimeter, bulk density is numerically equal to ap- 
parent specific gravity or volume weight. 

Cation Exchange.— The interchange of a cation in solution 
with another cation on a surface-active material. 

Cation-Exchange-Capacity.— The total quantity of cations 
which a soil can adsorb by cation exchange, usually ex- 
pressed as milliequivalents per 100 grams. Measured values 
of cation-exchange-capacity depend somewhat on the method 
used for the determination. 

Cell Constant. — See Conductivity-Cell Constant. 

Coefficient of Correlation. — A statistic used in linear corre- 
lation that provides a measure of the proportion of variation 
in one variable that is associated with variation in another 
variable. 

Coefficient of Determination. — A statistic used in linear 
correlation that gives the fraction of the variance in one vari- 
able which is associated with variance in another variable. It 
is the square of the coefficient of correlation and is usually 
expressed in percent. 

Coefficient of Variation. — Standard deviation expressed as 
percentage of the mean. 

Conductivity. — See Electrical Conductivity and Hydraulic 
Conductivity. 

Conductivity-Cell Constant (k) . — The product of the known 
electrical conductivity (EC) of a standard solution in a 
conductivity cell and the corresponding measured resistance 
(/?) of the cell containing the standard solution. That is: 
k=ECXR. The value of the cell constant is determined by 
the geometry of the cell and so is nearly independent of the 
temperature, but EC and R must be evaluated at the same 
temperature. Rearranging the equation and indicating tem- 
peratures by a subscript gives: ECt—k/Rt. In this form, the 
equation may be used for evaluating the conductivity ECt 
of an unknown solution in the cell at temperature (t), where 
Rt is the measured resistance of the cell containing the solu- 
tion at the temperature t and k is the cell constant as evalu- 
ated from a previous measurement of a standard solution. 

154 



Consumptive Use. — The water used by plants in transpiration 
and growth, plus water vapor loss from adjacent soil or snow 
or from intercepted precipitation in any specified time. 
Usually expressed as equivalent depth of free water per 
unit of time. 

Darcy's Law.— 1. Historical. The volume of water passing 
downward through a sand filter bed in unit time is propor- 
tional to the area of the bed and to the difference in hydraulic 
head and is inversely proportional to the thickness of the bed. 

2. Generalization for three dimensions. The effective rate of 
viscous flow of water in isotropic porous media is propor- 
tional to, and in the direction of, the hydraulic gradient. 

3. Generalization for other fluids. The effective rate of 
viscous flow of homogeneous fluids through isotropic porous 
media is proportional to, and in the direction of, the driving 
force. 

Dispersed Soil.— Soil in which the clay readily forms a colloidal 
sol. Dispersed soils usually have low permeability. They 
tend to shrink, crack, and become hard on drying and to slake 
and become plastic on wetting. 

Drainage. — 1. The processes of the discharge of water from an 
area of soil by sheet or stream flow (surface drainage) and 
the removal of excess water from within soil by downward 
flow through the soil (internal drainage). 2. The means for 
effecting the removal of water from the surface of soil and 
from within the soil, i. e., sloping topography or stream chan- 
nels (surface drainage) and open ditches, underground tile 
lines, or pumped wells (artificial drainage). 

Drainage Requirements. — Performance and capacity specifi- 
cations for a drainage system, i. e., permissible depths and 
modes of variation of the water table with respect to the root 
zone or soil surface, and the volume of water that the drains 
must convey in a given time. 

Efficiency of Irrigation. — The fraction of the water diverted 
from a river or other source that is consumed by the crop, 
expressed as percent. See Consumptive Use. Often applied 
to whole irrigation systems and takes account of conveyance 

losses. 

Efficiency of Water Application. — The fraction of the water 
delivered to the farm that is stored in the root zone for use 
by the crop, expressed as percent. 

Electrical Conductivity. — The reciprocal of the electrical 
resistivity. The resistivity is the resistance in ohms of a 
conductor, metallic or electrolytic, which is 1 cm. long and 
has a cross-sectional area of 1 cm. 2 Hence, electrical con- 
ductivity is expressed in reciprocal ohms per centimeter, or 
mhos per centimeter. The terms "electrical conductivity" 
and "specific electrical conductance" have identical meaning. 

Equivalent ; Equivalent Weight. — The weight in grams of an 
ion or compound that combines with or replaces 1 gm. of 
hydrogen. The atomic weight or formula weight divided by 
its valence. 

Equivalent Per Million. — An equivalent weight of an ion or 
salt per 1 million gm. of solution or soil. For solutions, 
equivalents per million (e. p. m.) and milliequivalents per 
liter (meq./l.) are numerically identical if the specific gravity 
of the solution is 1.0. 

Ethylene Glycol Retentivity. — Weight of ethylene glycol 
adsorbed per unit weight of soil under specified equilibrium 
or quasi-equilibrium conditions. See Method 25. 

Exchange Capacity. — See Cation-Exchange-Capacity. 

Exchange Complex. — The surface-active constituents of soils 
(both inorganic and organic) that are capable of cation 
exchange. 

Exchangeable Cation. — A cation that is adsorbed on the ex- 
change complex and which is capable of exchange with other 
cations. 



SALINE AND ALKALI SOILS 



155 



Exchangeable-Sodium-Percentage. — The degree of saturation 
of the soil exchange complex with sodium. It may be calcu- 
lated by the formula : 

Exchangeable sodium (meq./lOO gm. soil) 



ESP= 



Cation-exchange-capacity (meq./lOO gm. soil) 



XlOO 



Field Capacity. — The moisture content of soil in the field 2 or 3 
days after a thorough wetting of the soil profile by rain or 
irrigation water. Field capacity is expressed as moisture 
percentage, dry-weight basis. 

Fifteen-Atmosphere Percentage. — The moisture percentage, 
dry-weight basis, of a soil sample which has been wetted and 
brought to equilibrium in a pressure-membrane apparatus at 
a pressure of 221 p. s. i. This characteristic moisture value 
for soils approximates the lower limit of water available for 
plant growth. 

Fifty Percent Yield-Decrement Value. — The measured value 
of the soil salinity or alkali that decreases crop yield 50 
percent as compared with yields of the same crop on non- 
saline and nonalkali soils under similar growing conditions. 

Ground Water.— Water in soil beneath the soil surface, usually 
under conditions where the pressure in the water is greater 
than the atmospheric pressure, and the soil voids are sub- 
stantially filled with the water. 

Hydraulic Conductivity. — The proportionality factor in the 
Darcy flow law, which states that the effective flow velocity is 
proportional to the hydraulic gradient. Hydraulic conduc- 
tivity, therefore, is the effective flow velocity at unit 
hydraulic gradient and has the dimensions of velocity 
(LT 1 ). 

Hydraulic Gradient. — The decrease in hydraulic head per unit 
distance in the soil in the direction of the greatest rate of 
decrease of hydraulic head. 

Hydraulic Head. — The elevation with respect to a standard 
datum at which water stands in a riser or manometer con- 
nected to the point in question in the soil. This will include 
elevation head, pressure head, and also the velocity head, if 
the terminal opening of the sensing element is pointed up- 
stream. For nonturbulent flow of water in soil the velocity 
head is negligible. In unsaturated soil a porous cup must be 
used for establishing hydraulic contact between the soil 
water and water in a manometer. Hydraulic head has the 
dimensions of length (L). 

Indicator Plant. — A native plant that indicates, in general, 
and often in a specific manner, the nature of soil conditions 
with regard to moisture and salinity. Dominant species are 
the most important indicators of such conditions. 

Infiltration. — The downward entry of water into soil. 

Infiltration Rate; Infiltration Capacity. — The maximum 
rate at which a soil, in a given condition at a given time, can 
absorb rain. Also, the rate at which a soil will absorb water 
ponded on the surface at a shallow depth when the ponded 
area is infinitely large or when adequate precautions are taken 
to minimize the effect of divergent flow at the borders. It is 
the volume of water passing into the soil per unit of area 
per unit of time, and has the dimensions of velocity {LT' 1 ) . 

Intake Rate; Infiltration Velocity. — The rate of water 
entry into the soil expressed as a depth of water per unit of 
time. This term involves no restrictions on area of appli- 
cation or divergence of flow in the soil ; therefore, the measur- 
ing procedure should be specified. It has the dimensions of 
velocity (LT 1 ). 

Intrinsic Permeability. — The factor k' in the equation, 

k'dgi k' . ,_ , 

v = - = — {dFg-Vy) 

V V 

where v=flow velocity, e?=density, g— scalar value for ac- 
celeration of gravity, i=hydraulic gradient, 7?=viscosity, 
Fg~ gravitational force per unit of mass, and V p— pressure 
gradient. Intrinsic permeability has the dimensions of 
length squared {V) . See Permeability (Quantitative). 
Isobath. — 1. Having constant depth. 2. A line connecting 
points of equal depth to water table. 



Isopleth. — 1. A graph showing the occurrence or frequency of 
any phenomenon as a function of two variables. 2. A line 
showing the variation in time and position along a field profile 
of the point of intersection of a water-table contour line and 
the profile. 

Leaching. — The process of removal of soluble material by the 
passage of water through soil. 

Leaching Requirement. — The fraction of the water entering 
the soil that must pass through the root zone in order to 
prevent soil salinity from exceeding a specified value. Leach- 
ing requirement is used primarily under steady-state or long- 
time average conditions. 

Lime. — Strictly, calcium oxide (CaO), but as commonly used 
in agriculture terminology calcium carbonate (CaC0 3 ) and 
calcium hydroxide (Ca(OH) 2 ) are included. Agricultural 
lime refers to any of these compounds, with or without mag- 
nesia, used as an amendment for acid soils. 

Milliequivalent. — One thousandth of an equivalent. 

Milliequivalent Per Liter. — A milliequivalent of an ion or a 
compound in 1 liter of solution. 

Moisture Percentage. — 1. Dry- weight basis. The weight of 
water per 100 units of weight of material dried to constant 
weight at a standard temperature. 2. Depth basis. The 
equivalent depth of free water per 100 units of depth of soil. 
Numerically this value approximates the volume of water per 
100 units of volume of soil. 

Nonsaline-Alkali Soil. — A soil that contains sufficient ex- 
changeable sodium to interfere with the growth of most crop 
plants and does not contain appreciable quantities of soluble 
salts. The exchangeable-sodium-percentage is greater than 
15 and the electrical conductivity of the saturation extract is 
less than 4 millimhos per centimeter (at 25° C). The pH 
reading of the saturated soil paste is usually greater than 8.5. 

One-Third-Atmosphere Percentage. — The moisture percent- 
age, dry-weight basis, of a soil sample that has been air-dried, 
screened, wetted, and brought to hydraulic equilibrium with 
a permeable membrane at a soil-moisture tension of 345 cm. 
of water. This retentivity value closely approximates the 
moisture equivalent value of many soils. 

Osmotic Pressure. — The equivalent negative pressure that in- 
fluences the rate of diffusion of water through a semiper- 
meable membrane. Its direct experimental value for a solu- 
tion is the pressure difference required to equalize the diffu- 
sion rates between the solution and pure water across a 
semipermeable membrane. Osmotic pressure in atmospheres 
may be calculated from the freezing-point depression AT" 
in °C. by the formula OP=-~ 12M&T—0.021AT 2 . 

Particle Density.— The average density of the soil particles. 
Particle density is usually expressed in grams per cubic centi- 
meter and is sometimes referred to as "real density" or "grain 
density." 

Percolation. — A qualitative term applying to the downward 
movement of water through soil. Especially, the downward 
flow of water in saturated or nearly saturated soil at hydraulic 
gradients of one or less. 

Permanent Wilting Percentage. — The moisture percentage 
of soil at which plants wilt and fail to recover turgidity. It 
is usually determined with dwarf sunflowers. The expression 
has significance only for nonsaline soils. 

Permeability. — 1. Qualitative. The quality or state of a po- 
rous medium relating to the readiness with which such a 
medium conducts or transmits fluids. 2. Quantitative. The 
specific property governing the rate or readiness with which 
a porous medium transmits fluids under standard conditions. 
The equation used for expressing the flow should take into 
account the properties of the fluid so that proper measure- 
ments on a given medium give the same permeability value 
for all fluids that do not alter the medium. The physical 
dimensions of the permeability unit are determined by the 
equation used to express the flow. See Intrinsic Permeability. 

Plant Community. — An assemblage of plants living together 
under the same environmental conditions. 



156 



AGRICULTURE HANDBOOK 60, U. S. DEPT. OF AGRICULTURE 



Porosity. — The fraction of the soil volume not occupied by 
soil particles, i. e., the ratio of the sum of the volumes of the 
liquid and gas phases to the sum of the volumes of the solid, 
liquid, and gas phases of the soil. 

Potassium-Adsorption-Ratio. — A ratio for soil extracts and 
irrigation waters used to express the relative activity of 
potassium ions in exchange reactions with soil. 



PAR= 



K + 



V(Ca ++ +Mg ++ )/2 

where the ionic concentrations are expressed in milliequiva- 

lents per liter. 

Reclamation. — The process of removing excess soluble salts or 
excess exchangeable sodium from soils. 

Regression Coefficient. — A statistic used in linear correlation 
that gives the change in one variable that is associated with 
unit change in another variable. 

Saline-Alkali Soil.— A soil containing sufficient exchangeable 
sodium to interfere with the growth of most crop plants and 
containing appreciable quantities of soluble salts. The ex- 
changeable-sodium-percentage is greater than 15, and the 
electrical conductivity of the saturation extract is greater 
than 4 mmhos per centimeter (at 25° C). The pH reading 
of the saturated soil is usually less than 8.5. 

Saline Soil. — A nonalkali soil containing soluble salts in such 
quantities that they interfere with the growth of most crop 
plants. The electrical conductivity of the saturation extract 
is greater than 4 mmhos per centimeter (at 25° C), and the 
exchangeable-sodium-percentage is less than 15. The pH 
reading of the saturated soil is usually less than 8.5. 

Salinization. — The process of accumulation of soluble salts 
in soil. 

Saturated Soil Paste, — A particular mixture of soil and water. 
At saturation the soil paste glistens as it reflects light, flows 
slightly when the container is tipped, and the paste slides 
freely and cleanly from a spatula for all soils except those 
with high clay content. 

Saturation Extract.— The solution extracted from a soil at its 
saturation percentage. 

Saturation Percentage. — The moisture percentage of a 
saturated soil paste, expressed on.%a dry-weight basis. 

Semipermeable Membrane. — A membrane that permits the dif- 
fusion of one component of a solution but not the other. In 
biology, a septum which permits the diffusion of water but 
not of the solute. 



Sodium-Adsorption-Ratio. — A ratio for soil extracts and irri- 
gation waters used to express the relative activity of sodium 
ions in exchange reactions with soil. 

Na + 

S ^ = V7Ca ++ -fMg ++ )/2 

where the ionic concentrations are expressed in milliequiva- 
lents per liter. 

Soil Extract. — The solution separated from a soil suspension 
or a soil at a particular moisture content. 

Soil-Moisture Stress. — The sum of the soil-moisture tension 
and the osmotic pressure of the soil solution. It is the suc- 
tion or negative pressure to which water must be subjected 
to be at equilibrium through a semipermeable membrane 
with the solution in soil. 

Soil-Moisture Tension. — The equivalent negative pressure or 
suction of water in soil. Experimentally, the suction of water 
in soil is the pressure difference required across a permeable 
membrane to produce hydraulic equilibrium between the soil 
water and free water. 

Soluble-Sodium Percentage. — A term used in connection with 
irrigation waters and soil extracts to indicate the proportion 
of sodium ions in solution in relation to the total cation con- 
centration. It may be calculated by the formula: 

Soluble sodium concentration (meq./l.) 



SSP- 



xioo 



Total cation concentration (meq./l.) 

Specific Ion Effect. — Any effect of a salt constituent in the 

substrate on plant growth that is not caused by the osmotic 

properties of the substrate. 
Specific Surface. — The surface area, per unit weight of soil, 

commonly expressed as square meters per gram of soil 

(m. 2 /gm.). 

Standard Atmosphere. — A unit of pressure defined as follows: 
1 atmosphere— 1.013 XlO 6 dynes per sq. cm.= 14.71 pounds 
per sq. in. =76.39 cm. of mercury column =1,036 cm. of water 
column =34.01 ft. of water column. (Water and mercury 
at 20° C.) . 

Standard Deviation. — A statistic used to measure the disper- 
sion of a set of values around their mean. 

Suction. — See Soil-Moisture Tension. 

Water Table. — The upper boundary for ground water. The 
upper surface of the locus of points at which the pressure in 
the ground water is equal to atmospheric pressure. 



Appendix 



EC 

EC X10 3 

ECxlO* 

ACe 

fid, AGs, tiCm 

ECiw 

EC^y 

EC* 

R* 

mho 

mmho 

juraho 

ESP 

SAR 

EPP 

PAR 

CEC 

meq 

mg./l 

p. p. m 

pHs; pHe; pHi; pH 5 — 



Symbols and Abbreviations 

Electrical conductivity in mhos/cm. LR Leaching requirement. 

unless otherwise specified. HC Hydraulic conductivity. 

Electrical conductivity in millimhos/ PWP Permanent-wilting percentage. 

cm. (value in mhos/cm. X 10 3 ) . FAP Fifteen-atmosphere percentage. 

Electrical conductivity in micromhos/ SP Saturation percentage. 

cm. (value in mhos/cm. X 10'). SMT Soil-moisture tension. 

Electrical conductivity of saturation OP Osmotic pressure. 

extract QPe Osmotic pressure of saturation extract. 

Electrical conductivity of extract from AT Freezing-point depression, °C. 

a suspension having the proportions Pw Percentage water, dry-weight basis. 

of 1 gm. of dry soil to 1, 5, or 50 P* Percentage water, depth basis. 

gm. of water. d* Density of water. 

Electrical conductivity of irrigation d* Bulk density of soil. 

water dp Particle density of soil. 

Electrical conductivity of drainage k Hydraulic conductivity; conductivity- 

water or soil solution at the bottom cell constant. 

of the root zone. k' Intrinsic permeability. 

Electrical conductivity of saturated soil Z)iw . Depth of irrigation water applied to 

Resistance of soil paste in Bureau of Z?dw Depth (equivalent free depth) of 

Soils cup. „ drainage water. 

Reciprocal ohm; (ohm spelled back- D™ Consumptive use expressed as equiva- 

war d). lent free depth of water in a 

Millimho. specified time. 

Micromho. E Efficiency of irrigation water applica- 

Exchangeable-sodium-percentage. tion. 

Sodium-adsorption-ratio. n Porosity. 

Exchangeable-potassium-percentage. C2-S3 Example of classification of irrigation 

Potassium-adsorption-ratio. water; C denotes conductivity (eiec- 

Cation-exchange-capacity. trical) ; S denotes sodium (MK) ; 

Milliequivalent. numbers denote respective numen- 

Milligrams of solute per liter of solu- cal quality classes. (See ch. 5.) 

tion. m Meter. 

Parts per million. As commonly meas- cm Centimeter. 

ured and used parts per million is mm Millimeter. 

numerically equivalent to milligrams mfi Millimicron. 

per liter. \i Micron (10- 6 meter); also prefix 

pH reading of saturated soil paste; micro. 

saturation extract; 1 : 1 or 1 : 5 soil- A Angstrom (10" meter). 

water suspension. Measured with RCF Relative centrifugal force. 

glass electrode unless otherwise r. p. m Revolutions per minute. 

specified. V Viscosity. 



Conversion Formulas and Factors 



Conductivity to milliequivalent per liter : 

meq./l. = 10 X£CX10 3 , for irrigation waters and soil extracts 
in the range from 0.1 to 5.0 millimhos per cm. See figures 
4 and 20. 
Conductivity to osmotic pressure in atmospheres : 

OP=0.S6XECX 10 3 for soil extracts in the range from 3 to 30 
millimhos/cm. 
Conductivity to parts per million : 

p. p. m.=0.64X£CX10 6 for irrigation waters in the range 
100 to 5,000 micromhos/cm. 
Parts of salt per million parts of irrigation water to tons of 
salt per acre-loot of water: 
Tons per acre- foot (t. a. f. ) =0.00136 X P- P- m. 
Grains per gallon to parts per million: 

p. p. m.=17.lX grains per gallon. 
Milliequivalents per liter (from chemical analyses) to parts 
per million: 
Multiply meq./l. for ea<5h ion by its equivalent weight and 
obtain the sum. 



Gypsum (CaS0 4 -2H 2 0) equivalent weight=86.09 gm. 
Saturated gypsum solution at 25° C. contains: 
30.5 meq./l. ; 2.63 gm./l.; 2,630 p. p. m.; 3.5 tons of gypsum 
per acre-foot of water. One milliequivalent of gypsum per 
100 gm. of soil corresponds to 1.72 tons of gypsum per 
acre-foot of soil (4,000,000 lb.). In other words, tons of 
gypsum per acre-foot of soil=1.72X (milliequivalents gyp- 
sum per 100 gm. of soil). £CX10 3 =2.205 at 25° C. 
1 standard atmosphere = 1.013 XlO 6 dynes cm.- 2 ; 14.71 lb. 
in. 2 ; 76.39 cm. of mercury column; 1,036 cm. of water 
column; 34.01 ft. of water column. (Mercury and water 

at 20° C.) 
1 bar =10* dynes cm." 2 =1,023 cm. of water column. 
1 millibar=one thousandth of a bar. 
1 mile =5,280 feet. 
1 inch =2.54 cm. 
1 foot=30.48 cm. 
1 pound =453.59 gm. 
1 acre =43,560 sq. ft. 

157 



158 



AGRICULTURAL HANDBOOK 60, U. S. DEPT. OF AGRICULTURE 



1 acre-foot soil weighs 4,000,000 pounds (approximate). 
1 acre-foot water weighs 2,720,000 pounds (approximate) . 
Gallons per minute to cubic feet per second : 

c. f. s.=0.002228Xg- p.m. 
1 cubic foot per second (c. f. s.) = 

50 miner's inches in: Idaho, Kansas, Nebraska, Nevada, INew 
Mexico, North Dakota, South Dakota, Utah, and southern 
California. 
40 miner's inches in: Arizona, California (statute), Montana, 

and Oregon. 
38.4 miner's inches in: Colorado. 



1 c. f. s. for 24 hours=1.98 acre-feet. 
1 U. S. gallon=231 cubic inches, 

8.345 pounds of water. 

0.1337 cubic foot. 

58,417 grains of water. 
1 cubic foot =7.48 gallons. 
1 cubic foot of water weighs 62.43 lbs. 
1 cubic foot of soil in place weighs 68 to 112 pounds. Bulk 

density 1.1 to 1.8 gm. cmr 3 . 
Average particle density =2.65 gm. cm. -3 , approximately. 

(For soils which are low in organic matter.) 



Chemical symbols, equivalent weights, and 

common names 



Chemical symbol 
or formula — 



Ions: 

Ca ++ 

Mg ++ 

Na+ 

K+ 

CI" 

S0 4 — 

CO3— 

HCOr 

Salts: 

CaCl2 

CaS0 4 

CaS0 4 -2H 2 ... 

CaC0 3 

MgCl 2 

MgS0 4 

MgCOa 

NaCl 

Na 2 S0 4 

Na 2 CO b 

NaHCO a 

KC1 

K 2 S0 4 

K,C0 3 

KHC0 3 

Chemical amend 
ments: 

S 

H2SO1 

A1 2 (S0 4 ) 3 18H 2 

FeS0 4 7H 2 0... 



Equivalent 
weight 



Grams 

20.04 
12.16 
23.00 
39.10 
35.46 
48.03 
30.00 
61.01 

55.50 
68.07 
86.09 
50.04 
47.62 
60.19 
42.16 
58.45 
71.03 
53.00 
84.01 
74.56 
87.13 
69.10 
100. 11 



16.03 

49.04 

111.07 

139. 01 



Common name 



Calcium ion. 
Magnesium ion. 
Sodium ion. 
Potassium ion. 
Chloride ion. 
Sulfate ion. 
Carbonate ion. 
Bicarbonate ion. 

Calcium chloride. 
Calcium sulfate. 
Gypsum. 

Calcium carbonate. 
Magnesium chloride. 
Magnesium sulfate. 
Magnesium carbonate. 
Sodium chloride. 
Sodium sulfate. 
Sodium carbonate. 
Sodium bicarbonate. 
Potassium chloride. 
Potassium sulfate. 
Potassium carbonate. 
Potassium bicarbonate. 



Sulfur. 
Sulfuric acid. 
Aluminum sulfate. 
Iron sulfate (ferrous). 



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BRIQUET SUPPORT AND 
KNIFE EDGE ASSEMBLY 



90 Mitered joint 
(Brazed) 



End screen hare 
and solder to pipe 




Soft solder all joints 
while clamped to a 
milled aluminum template 



No. 29 Drill- 8-32 NC^ 
jr Deep 




No. 19 Drill - 82" CSK 
5 r 



No. 29 Drill - 8-32 N.C 



16 



2 Holes 



1 



at 



f\*\ C'Sor 

^4- J,*' lOIOtt 



■| Steel Boll-"u-Drill 



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1 


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1... 


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Drill 



BEAM 

2j Alum.- I Req'd 



® Aium.-iReq/d ADJUSTABLE END POST 




No. 19 Drill- 82 CSK to 
-% D. 4 Holes 



16 






X 



Moo 



s* 



No. 29 Drill - B-32 N.C. 
5- Deep 

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+0r 



§2 



16 



'16 




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COUNTERBALANCE 

(s) Brass- I Req'd 



16 



Drill 



"Sponge Rubber 



I- 1 
'8 




Ji4 



'F : 



No. 19 Drill- 82* CSK to ^D 
2 Holes b 



tt^r 



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"<- i 



= w=^„ Ttfffl 11 



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BASE KNIFE EDGE ( fixed ) 

5) Brass- I Req'd 



-rtr 
_4i_ 



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— 1- Drill- ^ C'Bore ^ Deep 
*H ^ o o 



— No. 29 Drill- 8-32 NC 

BASE KNIFE EDGE (swivel) 

&) Brass - (2 pieces) I unit Req'd 



-I* 



_>4JJ 1 JL 

^8 "*TNo.7 Drill- X" 



20NC 



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■— L 



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-No 29 Drill- 8-32 NC 
2 Holes 



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Sponge 
bber 



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BASE 
(7) Alum. - I Req'd 



END POST 



r7\ cinu ruo 
W Alum.- I Req'd 



'No. 29 Drill- 8-32 NC - 2 Holes 

BEAM KNIFE EDGE (swivel) 

(7) Brass- (2 pieces) I unit Req'd. 





v 



4-1 




(15) DRYING TRAY 
TGolvanized ptpe and Wire screen) 



TREMIE 
(Brass) 




BRIQUET MOLD 
(l6) (Brass) 



"S 
STRIKE-OFF TOOL 
(Hacksaw blodes) 




(9) Round head machine screw - 8-32NC x 2jj- 

^\ 1 * 1 " 

Qo)Pin, adj. end post il* 2 4~ 

MMPin, knife edges h*v& 

(j2) Fillister head machine screw «20NGx l" 

(j3)Nut, hexagon 



-±--20 NC 

4 



3" 



14) Flat head machine screw 8-32 NC x tt 

- J (kntfe edges) ,, 

17) Flat head machine screw 8-32 NCXj 
(end post) 



I Req'd. 

1 " 

2 » 
2 " 

1 " 
6 •' 

2 » 



MODULUS OF RUPTURE APPARATUS 



SOAKING TANK 
(Metal or Wood) 



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SALINE AND ALKALI SOILS 



159 




14 — 



^-<2J 






CO 



CO 



2t °- D 
16 Th'ds/m. 




CO 



16 



DRIVING HAMMER 
„_ „ 2.166" appr o x .^ 



8 



~ J3 W 
- J7 ~—- 1 o 



17- 



18- 



19 



Note: 

MACHINE TO ACCOMODATE 
RETAINER CYLINDERS - FREE 
SLIDING FIT. 




RETAINER CYLINDERS 



SOIL RETAINER ASSEMBLY 



Note; 

INSIDE DIAMETER OF CUTTING 
EDGE MUST BE 0.003° SMALLER 
THAN INSIDE DIAMETER OF 
RETAINER CYLINDERS. 




No. 


NAME 


SIZE 


No. 


MATERIAL 


1 


Handles 


l" 
T 


2 


Pipe, galvanized iron 


2 


Handle, fitting 


i " 

T 




Cross, - " 


3 


Handle, stem 


1 " 

J 




Pipe, » » 


4 


Cap , core sampler 


i " 
t 




Plate, mild steel 


5 


Barrel, core sampler 


II u 

2£*re w0 " 




Seamless tubing, steel 


6 


Cutting edge 


£«.0I0" 




Blued clock spring steel 


7 


Retainer disk 


i." 

s 




Plostic 


8 


U II 


3" 
16 




Ceramic 


9 


Rubber band 


#30 


2 




10 


Wire, retainer disk 


19 go. 




Wire, nichrome 


II 


Block f core extractor 


nominal 
2"x2" 


1 


Wood, pine 


12 


Fingers, core extractor 


1 " 

T 


2 


Rod, tobin bronze 


13 


Finger depressor ring 


2" 


1 


Thinwatl conduit 


14 


Head, hammer 


Zfdio. 


1 


Mild steel 


15 


Guide, hammer 


f«* 


1 


K ■ 


16 


Retainer cylinder 


2^*19 go. 


1 


Seamless tubing, brass 


17 


H ii 


■I 


2 


ii it H 


18 


>i ii 


■I 


2 


ii ii H 


19 


<■ H 


u 


1 


II l< H 



CORE EXTRACTOR 



Soil sampler and core retainer.